Regrowth for NeoForge currently supports up to version 1.20.2. Are there any plans to update it for 1.21.x?

Probably not before august 2025.

I'm currently swamped and having eye surgery at the start of march. We only have one neoforge mod ( Spider Pig) but the proof of technology has been done.

1.21.5 is just around the corner and that's another 20ishconversions.