After changing my gamertag, it still has not updated in the Xbox Console Companion, nor in...

Ah right. Removing as in just logging out on the xbox console companion app or removing the app entirely?

It can be just a glitch. I'd suggest checking the change on the Xbox website. If your new gamertag appears there, Then you might just need to remove your account and check again.

Yes, please try logging out and back in to your account see if the issue is fixed.

Same here, except i have Standard Game Pass.

The store has pre-installed (before the official launch) 90Go (or so) from the 150Go initially announced, but after that he has never downloaded nor installed the 60 Go left, so i suspect this is the reason FS is still asking for the disc.

And i can't find anyway to verify it or manually update the game from the store or Xbox companion or anything else

Hello, are you able to try changing your Gamertag through the Xbox Companion App on a Windows PC or directly through your Xbox console (if you have one)? If so, I'd advise changing the Gamertag through there for the time being.