urbanriot Rumours suggest that once it’s activated to Windows 11 that it will permanently be a Windows 11 key but I can’t prove that since it’s just rumours.
Nope, It is still useable for win10 on the same machine with the same hardware. BTDT.
ETA: From what I can tell, Win11 is really Win10.1. The core OS is the same with an updated user interface. If you use a third party start button like Start11, Open Shell or StartAllBack, you can make Win11 look a lot like Win7 or Win10. You can get all of the menus you are familiar with like Control Panel and Administrative Tools all from the start menu. With a few regedit tweaks, you can make File Explore Right Click look just like Win10. You can make Print Screen copy like Win10. With my systems, I can hardly tell the difference.