With the browser plugin uBlock Origin, you can block shares from Instagram with the custom rule:

www.facebook.com##.html-div:has(a[href*="www.instagram.com"])

Note: Facebook changes their css often. This may not work for long.

Also, uBlock Origin is not always the fastest plugin, you may see the Instagram posts briefly on your screen before it removes them.

How to Block Instagram Shares from Facebook Using uBlock Origin: A Complete Guide

Social media platforms have become increasingly interconnected, with content from one platform frequently appearing on another. For Facebook users, this often means encountering Instagram shares in their news feed—sometimes from accounts they follow on both platforms, creating redundant content, and sometimes from accounts they don't follow on Instagram at all, courtesy of Facebook's algorithmic recommendations.

If you're looking to curate a cleaner Facebook experience by filtering out these Instagram cross-posts, browser extensions like uBlock Origin offer a powerful solution through custom…