Hello, i'm writing here an issue related to iris shaders and gpu performance here too desperate to fix.

I play the pure version with sodium 0.6.0 beta 2 and iris 1.8.0 beta 4. When playing with shaders, the video card is not loaded above 20-30%, while it produces like 10 FPS and makes the game unplayable. Everything is fine on Optifine, the video card loads 80-100% and produces good FPS.

It is maybe an iris broken thing, because i have my drivers updated and minecraft is using my graphic card.

This is what happens if i turn on shaders on iris:

And the same shader but with optifine:

i do not know why this happens, unfortunately. A shader cannot intentionally under-utilize the GPU/control utilization like that.
it would probably be better to ask iris or sodium support about it.