I reused a Win10 Pro key from a mini PC from 2015 onto a brand new build and it worked right away. Not sure what the difference is with your situation. Maybe it was your license type?

You can buy a used mini PC for less than the price of a new Windows 11 license. I know there are cheaper license sites out there (unclear how legit they are) but this way you get a Windows license and a spare PC to run Linux!