fabric-carpet-1.15.2-pre1-1.3.5+v200114
carpet-extra-1.15.2-pre1-1.3.5
log:
https://paste.ee/p/u6rZy

The conflict is with another mod that uses it and requires it. They should raise their priority if its important for them. AFAIK carpet already marks this mixin as optional, so once they make theirs more important all should work.