Let me explain:
I installed on a modpack, the two mod yung's + the api and when I launched it, everything was fine
The thing is, the cave doesn't generate (it's the vanilla cave in minecraft that generates) and the mineshaft doesn't generate.
Worse, the category for the mod bettercave was not displayed and with JEI, it does not find the block/item of the mod
It's like I never installed them
help me :(

Closing due to inactivity.

Help you without logs? To confirm - it does not display in the Mod Menu as well?
Not sure how Forge treats Fabric mods but Fabric can detect Forge mods and it just won't load them + print some info in the log. Check if you use the correct version for your modloader.

Yeah, double check you got the correct versions. Also, neither of those mods add any blocks, so they will not have any JEI entries.