Would you kindly port this mod to 1.21.3? Thanks. (I don't want to intrude on this port thing)

There will only be ports to major version updates for Minecraft from now on (eg 1.22)

Erm, is it OK if I port it to 1.21.3?

I mean if you make a pull request to make it a separate branch then sure I guess but just don't go publishing it outside of this mod's jurisdiction as things could get confusing for other people from there

Well I made it. But it's unfinished!