Is your feature request related to a problem? Please describe.
I'm not quite sure if lithium's already doing this (I apologize if it is and I'm just wasting everyone's time), but if it isn't I think it would be an easy and effective way to improve performance. It's related to this Minecraft bug (MC-228976). In short, Minecraft calculates entity collisions both on the server and the client, which is not ideal.

Describe the solution you'd like
If you disable client side entity collision nothing should changes for the user, except a nice performance boost.

Describe alternatives you've considered
There's already a mod doing this. Their Github, Modrinth, CurseForge. You could perhaps incorporate the mod or use parts of it or something similar. The author's tests show a jump from 10-16 fps to 24-29 fps when looking at a large number of entities.

If you disable client side entity collision nothing should changes for the user, except a nice performance boost

... and broken collision with some entities like shulkers.

I was about to ask this question really waiting for answer if this is implemented because i seen this in log that it was disabled and this bug is serious performance hog and will make xp farms obsolete

I don't think there is a way to implement this without causing issues. Therefore it won't be added to lithium