@KLE24 

To confirm, we were on Windows XP Professional but the QB desktop 2021 wasn't compatible so we purchased a new laptop for this specific QB desktop 2021 program. Windows 11 is the OS that was pre-installed on this computer.

Is Windows 10 fully compatible?

You can't downgrade your OS to Win 10 unless you purchase a new OS license to replace it on your new machine. I can run QB Desktop 2021 Premier and Enterprise on Win 11 Home without any issue.