litematica mod for 1.21.10 with the forge modloader.

Hi, I'm gonna build a world eater for a perimeter to make some farms but I heard its really hard to build a world eater without litematica. for like an hour I've been trying to find a way to get lightmatica in a existing 1.21.10 forge modpack using the forge modloader, but I cant find out how. does anybody know a way to get litematica in my existing modpack. I've tried using forgematica but even though it says it supports 1.21.10 and forge mod loader when I try to add it to my mod pack it says its an incompatible mod loader. some help would be greatly appreciated :)