I was 100% on the Official Microsoft Store using the built in Windows Store App. Thankfully, after some tech support using live-chat with MS, they were able to refund the purchase.
Unfortunately, the only 'fix' for this (for me anyway) was to reinstall Windows 11 using the edition i had a CD key for. Sadly, this has the effect of me losing my Windows 11 Pro upgrade which I purchased digitally via the MS store last year as my original key was for Windows 11 Home. I might yet try and get further support to get my Pro edition back but this has been so much hassle for something as simple as a BIOS update that I dont know if i want to bother.
It also puts into question digital keys from Microsoft since they dont provide you with a license key and just activate digitally, if you run into this issue and your BIOS seemingly wipes your UEFI or TPM keys, you lose your product. At least with physically purchased keys you have a CD key you can re-enter.
edit: As a side note, I did try the slmgr command and it didnt help. The MS support people also did some attempts using alternative keys. Whatever the BIOS upgrade did, it seems to break something pretty good.