You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser after Angular 12 update

[alsoicode]

🐞 Bug report

Command (mark with an x)

• new
• build
• serve
• test
• e2e
• generate
• add
• update
• lint
• extract-i18n
• run
• config
• help
• version
• doc

Is this a regression?

Yes. ng serve worked as expected using 11.2.11

Description

After updating to Angular 12 via the advanced instructions at https://update.angular.io/?l=3&v=11.0-12.0, ng serve now throws an error:

Error: /Users/btaylor/work/angular-apps/mdsl-authoring/assets/scss/_colors.scss:1:4: Unknown word
You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser

Error: /Users/btaylor/work/angular-apps/mdsl-authoring/assets/scss/custom-bootstrap.scss:1:1: Unknown word
You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser

Error: /Users/btaylor/work/angular-apps/mdsl-authoring/assets/scss/global.scss:296:12: Unknown word
You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser

Error: /Users/btaylor/work/angular-apps/mdsl-authoring/assets/scss/mdsl-composer/mdsl-composer-variables.scss:103:1: Unknown word
You tried to parse SCSS with the standard CSS parser; try again with the postcss-scss parser

🔬 Minimal Reproduction

I'm not sure if this issue is reproduce-able, but the contents of our Scss files are quite unremarkable. Example:

// _colors.scss

// Bootstrap Overrides
$text-secondary: #2E93B1;
$text-muted: #ccc;
$link-color: #2E93B1;

.text-secondary {
  color: $text-secondary !important;
}

// LabCorp UI Overrides
$theme-colors: (
  'primary': #003A70,
  'secondary': #2E93B1,
  'success': #155724,
  'danger': #790E1D,
  'warning': #C59C38,
  'info': #007A6E,
  'light': #EDF1F4,
  'dark': #0B1519,
);

// UI design colors
$primary: #007FA3;
$highlighted: #D57800;
$accent: #5F456F;
$accent-secondary: #808080;
$related: #D1EAF1;

🔥 Exception or Error

🌍 Your Environment

OS X 11.3.1 (Beta) using Node 14.17.0

Anything else relevant?

[alan-agius4]

Duplicate of #20812

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