most mods that add content only support 1.20.1 , mods like create fabric , valkyrien skies , etc.
would be nice if you support 1.20.1 until most modders update their mods to 1.21 or you can fix all the bugs in 1.20.1 0.5.1 and keep doing so until its stable enough ;D

would be really cool !

Sorry, I generally don't do backports except for critical security bugs.

The code's all here, though - feel free to do it yourself and send a PR.