Either I'm delusional, or I'm not.
Last night, I saw a 1.21.4 version for this mod and I was ecstatic. Now I can't find it anywhere.
Aside from that, are there plans for a 1.21.4 port?

I definitely haven't made one yet, but yes, the port is in progress. It is unfortunately not as quick or easy as I'd like, but it'll hopefully be done within the next couple of weeks.

Happy to say that the port is finally done :)