For whatever reason, Rubidium gets heavy fps drops, losing around 10 fps per tool, whenever a tetra tool is being displayed anywhere. Doesn't matter if it's in the inventory, in a chest, or in your hand, it'll cause the fps to drop. The issue is especially prevalent when multiple tetra tools are onscreen.

Here's some screenshots of this issue in action. https://imgur.com/a/t4yULVv
I assume it's caused by tetra tools essentially being composed of multiple layers, which for whatever reason causes issues with Rubidium's rendering.

Issue is still prevalent in 1.18.2.

Add 'mixin.features.item=false' into the rubidium config can fix this issue when playing.
reference:
https://mineyourmind.net/forum/threads/how-to-fix-broken-t-construct-item-textures.32974/

sry but have u solved the problem? i met the same problem