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!
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 no longer activate new Windows 11 builds with Windows 7 or 8 keys; maybe last chance to activate using Windows 7 or 8 keys, for 22H2. (www.neowin.net)