Don't use 1.21.0, use 1.21.1, not support will be fixing for 1.21.0

Originally posted by @AzureDoom in #14 (comment)

Is there something that the users of 1.20 can we do?, right now i can't change mi version to 1.21.1, I have the same problem in the loading screen.

No, this is due to neoforge changes that only apply to 1.21.1+