When I want to fully utilize datapacks and rescoure packs like incendium and stellarity it causes errors and the mobs don't work

The custom textures work with optifine, but I use lunar

Optifine but forge is bad for fps

CEM will never be implemented in Iris, and afaik nor Oculus.

On Fabric there is CEM which handles it

use EMF and ETF, CEM is broken and old
this feature will never be added in Iris.