FaceTime (still) not working - MacBook

Any good suggestions for getting FaceTime working? FaceTime used to work just fine until I changed computers. Since then, I've never had it working. By not working, I mean you try to sign in, everything looks just fine, but FaceTime just won't sign in .. the Apple ID is correct, no problems there.

I've tried all the usual stuff (please don't repost Apple links, I've tried all of them). My Preferences are gated out (yes, I've tried all suggestions, example: The FaceTime preferences is greyed out, h… - Apple Community), but nothing works. Interestingly, I have no FaceTime in my Cache folder, which might be something. I've searched (using Terminals -iname, but no luck). Lastly, I've tried recreating a new AppleiD, but that doesn't help either.

So, anyone out there with some new ideas, or maybe an apple employee with some knowledge?

I'd be most grateful, thanks in advance.

Although it should say so, I'm on a MacBook Pro early 2015 running Monterey - FaceTime also didn't run on Big Sur either!