diff --git a/packages/gatsby-plugin-cxs/src/__tests__/gatsby-node.js b/packages/gatsby-plugin-cxs/src/__tests__/gatsby-node.js
index 8494980faf068..e04d2ef2d5b19 100644
--- a/packages/gatsby-plugin-cxs/src/__tests__/gatsby-node.js
+++ b/packages/gatsby-plugin-cxs/src/__tests__/gatsby-node.js
@@ -3,13 +3,17 @@ import { testPluginOptionsSchema } from "gatsby-plugin-utils"
 import { pluginOptionsSchema } from "../gatsby-node"
 
 it(`should provide meaningful errors when fields are invalid`, async () => {
-  const expectedErrors = [`"optionA" is not allowed`]
+  const expectedWarnings = [`"optionA" is not allowed`]
 
-  const { errors } = await testPluginOptionsSchema(pluginOptionsSchema, {
-    optionA: `This options shouldn't exist`,
-  })
-
-  expect(errors).toEqual(expectedErrors)
+  const { warnings, isValid, hasWarnings } = await testPluginOptionsSchema(
+    pluginOptionsSchema,
+    {
+      optionA: `This options shouldn't exist`,
+    }
+  )
+  expect(isValid).toBe(true)
+  expect(hasWarnings).toBe(true)
+  expect(warnings).toEqual(expectedWarnings)
 })
 
 it.each`
diff --git a/packages/gatsby-plugin-flow/src/__tests__/gatsby-node.js b/packages/gatsby-plugin-flow/src/__tests__/gatsby-node.js
index 85934bc8380de..0bbae52fea874 100644
--- a/packages/gatsby-plugin-flow/src/__tests__/gatsby-node.js
+++ b/packages/gatsby-plugin-flow/src/__tests__/gatsby-node.js
@@ -19,17 +19,18 @@ describe(`onCreateBabelConfig`, () => {
 
 describe(`pluginOptionsSchema`, () => {
   it(`should provide meaningful errors when fields are invalid`, async () => {
-    const expectedErrors = [`"optionA" is not allowed`]
+    const expectedWarnings = [`"optionA" is not allowed`]
 
-    const { isValid, errors } = await testPluginOptionsSchema(
+    const { isValid, warnings, hasWarnings } = await testPluginOptionsSchema(
       pluginOptionsSchema,
       {
         optionA: `This option shouldn't exist`,
       }
     )
 
-    expect(isValid).toBe(false)
-    expect(errors).toEqual(expectedErrors)
+    expect(isValid).toBe(true)
+    expect(hasWarnings).toBe(true)
+    expect(warnings).toEqual(expectedWarnings)
   })
 
   it.each`
diff --git a/packages/gatsby-plugin-manifest/src/__tests__/gatsby-node.js b/packages/gatsby-plugin-manifest/src/__tests__/gatsby-node.js
index e9d1b8087969a..8c8412159bd27 100644
--- a/packages/gatsby-plugin-manifest/src/__tests__/gatsby-node.js
+++ b/packages/gatsby-plugin-manifest/src/__tests__/gatsby-node.js
@@ -532,12 +532,11 @@ describe(`Test plugin manifest options`, () => {
 
 describe(`pluginOptionsSchema`, () => {
   it(`validates options correctly`, async () => {
-    expect(await testPluginOptionsSchema(pluginOptionsSchema, manifestOptions))
-      .toMatchInlineSnapshot(`
-      Object {
-        "errors": Array [],
-        "isValid": true,
-      }
-    `)
+    const { isValid } = await testPluginOptionsSchema(
+      pluginOptionsSchema,
+      manifestOptions
+    )
+
+    expect(isValid).toBe(true)
   })
 })
diff --git a/packages/gatsby-plugin-sass/src/__tests__/gatsby-node.js b/packages/gatsby-plugin-sass/src/__tests__/gatsby-node.js
index 373fa2b35bb02..74a9e2554a293 100644
--- a/packages/gatsby-plugin-sass/src/__tests__/gatsby-node.js
+++ b/packages/gatsby-plugin-sass/src/__tests__/gatsby-node.js
@@ -170,10 +170,14 @@ describe(`pluginOptionsSchema`, () => {
   })
 
   it(`should allow unknown options`, async () => {
-    const { isValid } = await testPluginOptionsSchema(pluginOptionsSchema, {
-      webpackImporter: `unknown option`,
-    })
+    const { isValid, hasWarnings } = await testPluginOptionsSchema(
+      pluginOptionsSchema,
+      {
+        webpackImporter: `unknown option`,
+      }
+    )
 
     expect(isValid).toBe(true)
+    expect(hasWarnings).toBe(true)
   })
 })
diff --git a/packages/gatsby-plugin-sitemap/src/__tests__/options-validation.js b/packages/gatsby-plugin-sitemap/src/__tests__/options-validation.js
index d83f199342f67..3d9da3b7c81ff 100644
--- a/packages/gatsby-plugin-sitemap/src/__tests__/options-validation.js
+++ b/packages/gatsby-plugin-sitemap/src/__tests__/options-validation.js
@@ -3,25 +3,31 @@ import { testPluginOptionsSchema, Joi } from "gatsby-plugin-utils"
 
 describe(`pluginOptionsSchema`, () => {
   it(`should provide meaningful errors when fields are invalid`, async () => {
-    const expectedErrors = [`"wrong" is not allowed`]
+    const expectedErrors = [`"output" must be a string`]
 
-    const { errors } = await testPluginOptionsSchema(pluginOptionsSchema, {
-      wrong: `test`,
-    })
+    const { isValid, errors } = await testPluginOptionsSchema(
+      pluginOptionsSchema,
+      {
+        output: 123,
+      }
+    )
 
+    expect(isValid).toBe(false)
     expect(errors).toEqual(expectedErrors)
   })
 
-  it(`should provide error for deprecated "exclude" option`, async () => {
-    const expectedErrors = [
-      `As of v4 the \`exclude\` option was renamed to \`excludes\``,
-    ]
+  it(`should provide warning for deprecated "exclude" option`, async () => {
+    const expectedWarnings = [`"exclude" is not allowed`]
 
-    const { errors } = await testPluginOptionsSchema(pluginOptionsSchema, {
-      exclude: [`test`],
-    })
+    const { warnings, hasWarnings } = await testPluginOptionsSchema(
+      pluginOptionsSchema,
+      {
+        exclude: [`test`],
+      }
+    )
 
-    expect(errors).toEqual(expectedErrors)
+    expect(hasWarnings).toBe(true)
+    expect(warnings).toEqual(expectedWarnings)
   })
 
   it(`creates correct defaults`, async () => {
@@ -48,7 +54,7 @@ describe(`pluginOptionsSchema`, () => {
     ${undefined}
     ${{}}
   `(`should validate the schema: $options`, async ({ options }) => {
-    const { isValid } = await testPluginOptionsSchema(
+    const { isValid, errors } = await testPluginOptionsSchema(
       pluginOptionsSchema,
       options
     )
diff --git a/packages/gatsby-plugin-sitemap/src/options-validation.js b/packages/gatsby-plugin-sitemap/src/options-validation.js
index 4ebbdf319e081..66bdc13c87dfa 100644
--- a/packages/gatsby-plugin-sitemap/src/options-validation.js
+++ b/packages/gatsby-plugin-sitemap/src/options-validation.js
@@ -41,7 +41,8 @@ export const pluginOptionsSchema = ({ Joi }) =>
           }
         }`
       )
-      .external(({ query }) => {
+      .external(pluginOptions => {
+        const query = pluginOptions?.query
         if (query) {
           try {
             parseGraphql(query)
@@ -74,9 +75,6 @@ export const pluginOptionsSchema = ({ Joi }) =>
         enter other data types into this array for custom filtering.
         Doing so will require customization of the \`filterPages\` function.`
       ),
-    exclude: Joi.forbidden().messages({
-      "any.unknown": `As of v4 the \`exclude\` option was renamed to \`excludes\``,
-    }),
     resolveSiteUrl: Joi.function()
       .default(() => resolveSiteUrl)
       .description(
diff --git a/packages/gatsby-plugin-twitter/src/__tests__/gatsby-node.js b/packages/gatsby-plugin-twitter/src/__tests__/gatsby-node.js
index 8494980faf068..e340053e76973 100644
--- a/packages/gatsby-plugin-twitter/src/__tests__/gatsby-node.js
+++ b/packages/gatsby-plugin-twitter/src/__tests__/gatsby-node.js
@@ -3,13 +3,18 @@ import { testPluginOptionsSchema } from "gatsby-plugin-utils"
 import { pluginOptionsSchema } from "../gatsby-node"
 
 it(`should provide meaningful errors when fields are invalid`, async () => {
-  const expectedErrors = [`"optionA" is not allowed`]
+  const expectedWarnings = [`"optionA" is not allowed`]
 
-  const { errors } = await testPluginOptionsSchema(pluginOptionsSchema, {
-    optionA: `This options shouldn't exist`,
-  })
+  const { warnings, isValid, hasWarnings } = await testPluginOptionsSchema(
+    pluginOptionsSchema,
+    {
+      optionA: `This options shouldn't exist`,
+    }
+  )
 
-  expect(errors).toEqual(expectedErrors)
+  expect(isValid).toBe(true)
+  expect(hasWarnings).toBe(true)
+  expect(warnings).toEqual(expectedWarnings)
 })
 
 it.each`
diff --git a/packages/gatsby-plugin-utils/src/__tests__/index.ts b/packages/gatsby-plugin-utils/src/__tests__/index.ts
index e1c2e276ace0d..7b97c015cfdb9 100644
--- a/packages/gatsby-plugin-utils/src/__tests__/index.ts
+++ b/packages/gatsby-plugin-utils/src/__tests__/index.ts
@@ -1,5 +1,6 @@
 /* eslint-disable @typescript-eslint/explicit-function-return-type */
 import { validateOptionsSchema, Joi } from "../"
+import { testPluginOptionsSchema } from "../test-plugin-options-schema"
 
 it(`validates a basic schema`, async () => {
   const pluginSchema = Joi.object({
@@ -9,9 +10,9 @@ it(`validates a basic schema`, async () => {
   const validOptions = {
     str: `is a string`,
   }
-  expect(await validateOptionsSchema(pluginSchema, validOptions)).toEqual(
-    validOptions
-  )
+
+  const { value } = await validateOptionsSchema(pluginSchema, validOptions)
+  expect(value).toEqual(validOptions)
 
   const invalid = () =>
     validateOptionsSchema(pluginSchema, {
@@ -56,18 +57,38 @@ it(`does not validate async external validation rules when validateExternalRules
   expect(invalid).not.toThrowError()
 })
 
-it(`throws an error on unknown values`, async () => {
+it(`throws an warning on unknown values`, async () => {
   const schema = Joi.object({
     str: Joi.string(),
   })
 
-  const invalid = () =>
-    validateOptionsSchema(schema, {
+  const validWarnings = [`"notInSchema" is not allowed`]
+
+  const { hasWarnings, warnings } = await testPluginOptionsSchema(
+    () => schema,
+    {
       str: `bla`,
       notInSchema: true,
-    })
-
-  expect(invalid()).rejects.toThrowErrorMatchingInlineSnapshot(
-    `"\\"notInSchema\\" is not allowed"`
+    }
   )
+
+  expect(hasWarnings).toBe(true)
+  expect(warnings).toEqual(validWarnings)
+})
+
+it(`populates default values`, async () => {
+  const pluginSchema = Joi.object({
+    str: Joi.string(),
+    default: Joi.string().default(`default`),
+  })
+
+  const validOptions = {
+    str: `is a string`,
+  }
+
+  const { value } = await validateOptionsSchema(pluginSchema, validOptions)
+  expect(value).toEqual({
+    ...validOptions,
+    default: `default`,
+  })
 })
diff --git a/packages/gatsby-plugin-utils/src/test-plugin-options-schema.ts b/packages/gatsby-plugin-utils/src/test-plugin-options-schema.ts
index edd0e259b939c..83a4c8777db00 100644
--- a/packages/gatsby-plugin-utils/src/test-plugin-options-schema.ts
+++ b/packages/gatsby-plugin-utils/src/test-plugin-options-schema.ts
@@ -5,7 +5,9 @@ import { IPluginInfoOptions } from "./types"
 
 interface ITestPluginOptionsSchemaReturnType {
   errors: Array<string>
+  warnings: Array<string>
   isValid: boolean
+  hasWarnings: boolean
 }
 
 export async function testPluginOptionsSchema(
@@ -44,11 +46,22 @@ export async function testPluginOptionsSchema(
   })
 
   try {
-    await validateOptionsSchema(pluginSchema, pluginOptions)
+    const { warning } = await validateOptionsSchema(pluginSchema, pluginOptions)
+
+    const warnings = warning?.details?.map(detail => detail.message) ?? []
+
+    if (warnings?.length > 0) {
+      return {
+        isValid: true,
+        errors: [],
+        hasWarnings: true,
+        warnings,
+      }
+    }
   } catch (e) {
-    const errors = e.details.map(detail => detail.message)
-    return { isValid: false, errors }
+    const errors = e?.details?.map(detail => detail.message) ?? []
+    return { isValid: false, errors, hasWarnings: false, warnings: [] }
   }
 
-  return { isValid: true, errors: [] }
+  return { isValid: true, errors: [], hasWarnings: false, warnings: [] }
 }
diff --git a/packages/gatsby-plugin-utils/src/utils/plugin-options-schema-joi-type.ts b/packages/gatsby-plugin-utils/src/utils/plugin-options-schema-joi-type.ts
index c9811a58dc7fe..4336ca3aba599 100644
--- a/packages/gatsby-plugin-utils/src/utils/plugin-options-schema-joi-type.ts
+++ b/packages/gatsby-plugin-utils/src/utils/plugin-options-schema-joi-type.ts
@@ -1160,7 +1160,7 @@ interface AnySchema extends SchemaInternals {
    * Warnings are reported separately from errors alongside the result value via the warning key (i.e. `{ value, warning }`).
    * Warning are always included when calling `any.validate()`.
    */
-  warning(code: string, context: Context): this
+  warning(code: string, context?: Context): this
 
   /**
    * Converts the type into an alternatives type where the conditions are merged into the type definition where:
diff --git a/packages/gatsby-plugin-utils/src/validate.ts b/packages/gatsby-plugin-utils/src/validate.ts
index 3493481b07d31..8be0e3c39fdcb 100644
--- a/packages/gatsby-plugin-utils/src/validate.ts
+++ b/packages/gatsby-plugin-utils/src/validate.ts
@@ -1,5 +1,5 @@
 import { ValidationOptions } from "joi"
-import { ObjectSchema } from "./joi"
+import { ObjectSchema, Joi } from "./joi"
 import { IPluginInfoOptions } from "./types"
 
 const validationOptions: ValidationOptions = {
@@ -10,6 +10,20 @@ const validationOptions: ValidationOptions = {
 
 interface IOptions {
   validateExternalRules?: boolean
+  returnWarnings?: boolean
+}
+
+interface IValidateAsyncResult {
+  value: IPluginInfoOptions
+  warning: {
+    message: string
+    details: Array<{
+      message: string
+      path: Array<string>
+      type: string
+      context: Array<Record<string, unknown>>
+    }>
+  }
 }
 
 export async function validateOptionsSchema(
@@ -17,14 +31,19 @@ export async function validateOptionsSchema(
   pluginOptions: IPluginInfoOptions,
   options: IOptions = {
     validateExternalRules: true,
+    returnWarnings: true,
   }
-): Promise<IPluginInfoOptions> {
-  const { validateExternalRules } = options
+): Promise<IValidateAsyncResult> {
+  const { validateExternalRules, returnWarnings } = options
 
-  const value = await pluginSchema.validateAsync(pluginOptions, {
+  const warnOnUnknownSchema = pluginSchema.pattern(
+    /.*/,
+    Joi.any().warning(`any.unknown`)
+  )
+
+  return (await warnOnUnknownSchema.validateAsync(pluginOptions, {
     ...validationOptions,
     externals: validateExternalRules,
-  })
-
-  return value
+    warnings: returnWarnings,
+  })) as Promise<IValidateAsyncResult>
 }
diff --git a/packages/gatsby/src/bootstrap/load-plugins/__tests__/load-plugins.ts b/packages/gatsby/src/bootstrap/load-plugins/__tests__/load-plugins.ts
index 09203261f2ecc..192f457620b06 100644
--- a/packages/gatsby/src/bootstrap/load-plugins/__tests__/load-plugins.ts
+++ b/packages/gatsby/src/bootstrap/load-plugins/__tests__/load-plugins.ts
@@ -454,7 +454,7 @@ describe(`Load plugins`, () => {
       expect((reporter.warn as jest.Mock).mock.calls[0]).toMatchInlineSnapshot(`
         Array [
           "Warning: there are unknown plugin options for \\"gatsby-plugin-google-analytics\\": doesThisExistInTheSchema
-        Please open an issue at ghub.io/gatsby-plugin-google-analytics if you believe this option is valid.",
+        Please open an issue at https://ghub.io/gatsby-plugin-google-analytics if you believe this option is valid.",
         ]
       `)
       expect(mockProcessExit).not.toHaveBeenCalled()
diff --git a/packages/gatsby/src/bootstrap/load-plugins/validate.ts b/packages/gatsby/src/bootstrap/load-plugins/validate.ts
index b98c44ea0e6d8..a66b44559759f 100644
--- a/packages/gatsby/src/bootstrap/load-plugins/validate.ts
+++ b/packages/gatsby/src/bootstrap/load-plugins/validate.ts
@@ -282,6 +282,14 @@ async function validatePluginsOptions(
         }),
       })
 
+      // If rootDir and plugin.parentDir are the same, i.e. if this is a plugin a user configured in their gatsby-config.js (and not a sub-theme that added it), this will be ""
+      // Otherwise, this will contain (and show) the relative path
+      const configDir =
+        (plugin.parentDir &&
+          rootDir &&
+          path.relative(rootDir, plugin.parentDir)) ||
+        null
+
       if (!Joi.isSchema(optionsSchema) || optionsSchema.type !== `object`) {
         // Validate correct usage of pluginOptionsSchema
         reporter.warn(
@@ -300,11 +308,39 @@ async function validatePluginsOptions(
           })
         }
 
-        plugin.options = await validateOptionsSchema(
+        const { value, warning } = await validateOptionsSchema(
           optionsSchema,
           (plugin.options as IPluginInfoOptions) || {}
         )
 
+        plugin.options = value
+
+        // Handle unknown key warnings
+        const validationWarnings = warning?.details
+
+        if (validationWarnings?.length > 0) {
+          reporter.warn(
+            stripIndent(`
+        Warning: there are unknown plugin options for "${plugin.resolve}"${
+              configDir ? `, configured by ${configDir}` : ``
+            }: ${validationWarnings
+              .map(error => error.path.join(`.`))
+              .join(`, `)}
+        Please open an issue at https://ghub.io/${
+          plugin.resolve
+        } if you believe this option is valid.
+      `)
+          )
+          trackCli(`UNKNOWN_PLUGIN_OPTION`, {
+            name: plugin.resolve,
+            valueString: validationWarnings
+              .map(error => error.path.join(`.`))
+              .join(`, `),
+          })
+          // We do not increment errors++ here as we do not want to process.exit if there are only warnings
+        }
+
+        // Validate subplugins
         if (plugin.options?.plugins) {
           const { errors: subErrors, plugins: subPlugins } =
             await validatePluginsOptions(
@@ -322,21 +358,7 @@ async function validatePluginsOptions(
         }
       } catch (error) {
         if (error instanceof Joi.ValidationError) {
-          // Show a small warning on unknown options rather than erroring
-          const validationWarnings = error.details.filter(
-            err => err.type === `object.unknown`
-          )
-          const validationErrors = error.details.filter(
-            err => err.type !== `object.unknown`
-          )
-
-          // If rootDir and plugin.parentDir are the same, i.e. if this is a plugin a user configured in their gatsby-config.js (and not a sub-theme that added it), this will be ""
-          // Otherwise, this will contain (and show) the relative path
-          const configDir =
-            (plugin.parentDir &&
-              rootDir &&
-              path.relative(rootDir, plugin.parentDir)) ||
-            null
+          const validationErrors = error.details
           if (validationErrors.length > 0) {
             reporter.error({
               id: `11331`,
@@ -348,31 +370,6 @@ async function validatePluginsOptions(
             })
             errors++
           }
-
-          if (validationWarnings.length > 0) {
-            reporter.warn(
-              stripIndent(`
-                Warning: there are unknown plugin options for "${
-                  plugin.resolve
-                }"${
-                configDir ? `, configured by ${configDir}` : ``
-              }: ${validationWarnings
-                .map(error => error.path.join(`.`))
-                .join(`, `)}
-                Please open an issue at ghub.io/${
-                  plugin.resolve
-                } if you believe this option is valid.
-              `)
-            )
-            trackCli(`UNKNOWN_PLUGIN_OPTION`, {
-              name: plugin.resolve,
-              valueString: validationWarnings
-                .map(error => error.path.join(`.`))
-                .join(`, `),
-            })
-            // We do not increment errors++ here as we do not want to process.exit if there are only warnings
-          }
-
           return plugin
         }