A crash on loader 0.12.1: https://hastebin.com/isixedepes.yaml
Same crash on loader 0.11.7: https://hastebin.com/axomarowit.yaml

See https://fabricmc.net/2021/10/03/loader-0120.html#mixin-compatibility for more info on what exactly changed in loader in regards to 0.12.

I should probably have linked this earlier: SpongePowered/Mixin#529 will make it possible to fix this issue (should I PR it to Fabric's fork too?)

Finally updating my installed mods to 1.18.2 , is this still blocked?

Minecraft is now on 1.19, any plans on updating this?