Hi!
it seems the mod is working correctly with MC Version 1.21.1 but it is tagged in Modrinth and Curseforge as 1.21.

If it were tagged like geyser does it then it would be compatible with 1.21 and 1.21.1 which is what you want i believe.

Can you perhaps update the tag so launchers like Prism can correctly detect it is compatible with 1.21.1?