Hi,
I used System File Checker (SFC) to check and repair my installation. It said it didn't find any errors but my activation disappeared right after doing the check. I ended up having to download the most recent Windows 11 release, installing it, and activating it with my original key. That fixed all my issues. I think I had previously said I just rolled it back but that failed the next day when Windows Update decided I needed an update, etc. It sure seems like this issue comes about for a variety of reasons and there's not just 1 thing to fix it.