since 1.21 changes so much it would seem that one of the mixins no longer routes correctly and the game crashes on start. would love to see sfc updated to 1.21

It may take a long time to port to 1.21.
I tried to implement #2 on 1.20.1 but something was wrong and stuck me for several month now. Even worse my life is going busy recently. So...😩

unfinish port in a new repo for 1.21 and neoforge:
https://github.com/Rivmun/SuperFancyCloudsRearchitected
Mojang changed a lot of code in renderClouds(). Forgive my poor code skill, I don't know how to render SFC on correctly position yet.