Says it needs Java 21, but Java 17 is present. 1.20.1 uses Java 17 and cannot use Java 21

next alpha should be natively compatible w java 17. in the meantime just run the game with 21

It isn't possible to run 1.20.1 with Java21. That version of the mod is essentially bricked.

Java 21 works perfectly fine on 1.20.1.

That said, some launchers (notably Curseforge launcher) do not allow using using anything besides the Mojang-recommended Java version for a given game version, so this version is unusable with those launchers.

fixed in 8.0-alpha.2