Similar issue here, upgraded from Windows 10 to 11 no problem for almost two years and after a recent BIOS update ( I did multiple in the past without issue ) Win11 won't activate anymore.
I had linked the license to my MS account and now seeing:
Unable to activate Windows
We can't activate your copy of Windows because the digital licence for this device has already been used to reactivate Windows.
Sounds like the BIOS update just trigger hardware change and those reactivation are finite.
If only Windows could see it's the same hardware, just an updated BIOS.
This is going to impact security as people will be afraid of updating their BIOS even more :-(