Instagram and Tiktok quite literally insert "&USERID=2834790" crap into every URL you copy, and it's a string that's unique to you (either based on your account ID or a browser cookie) that doesn't change. They can absolutely tell whether you specifically are sharing certain things if you don't remove that.

You can't just make a blanket statement of "they aren't tracking you" - there are absolutely websites that assign you a thumbprint through a cookie in an attempt associate other browsing activity with your unique ID, and removing unique identifiers from URLs before you share is a simple way to remove access to some of that data.

I would suggest you look into data brokers if you don't think it's a big deal. They make browsing profiles for "unique user IDs" that are "totally anonymized" but when you combine datasets it can be TRIVIAL to tie a specific real person (name and address) to a browsing history / advertisement profile.