hello,

I'm playing on version 1.21.4 as far as I know the mod should be compatible with this version but for some reason I can not put a book into the grinder

I can put helmets and swords and all into it but no book help?

Yes, if you have version 4.0.0+1.21.4-rc3, the mod should be compatible. Is this happening in singleplayer? Multiplayer? If it's the latter, make sure the mod is installed on the server.