https://github.com/Chisel-Team/ConnectedTexturesMod/blob/19a58b080ff2d4fec4fd44ffdb426fc078ce853d/src/main/resources/ctm.mixins.json#L6 While this mod is a clientside mod, for some reason the 1.21.1 neoforge file is not marked client only (and some mods may mark this one as a dependency). It would make the logs cleaner if this mixin was in the client section so the mixin processor didnt try to target it on dedicated servers.