Amazon used to offer short links in their share link on item pages. But they stopped.
So here's a Chrome extension which does this for you. I'd publish it, but having experience with publishing Android aps, I'm tired of how Google keep changing the rules every time you want to make a bugfix. So I probably won't bother.
No warranty offered, use at your own risk.
Copyright (c) 2019 alertedsnake
Git clone this package somewhere, or download the zipfile and unpack it.
Next, in Chrome, navigate chrome://extensions/ and turn on Developer mode.
Use the Load unpacked button to install the extension by providing the directory with the unpacked extension, this is the directory which contains manifest.json, most likely named amzn-shrtnr.
Adjust these instructions as needed - the extension directory may end up buried in a subdirectory somewhere due to the unzipping process.
Go to an amazon product page and click the extension's icon. That's it.
Make sure you wait for the page to fully load.