(Note, most of this is extracted from my review on a fork of this mod, Brute Force Rendering Culling Revived, for 1.20.1.)

Brute Force Rendering Culling (and its 1.20.1 fork Revived) is the sole reason I can play the modpacks I love with a playable framerate. We're talking from 6-18 fps to a whopping 25-85 fps increase. (And yes, my laptop performs that poorly.)

What it does is simple: brute force rendering culling. If it's not on your screen, the mod will prevent it from rendering before it even reaches the CPU. This applies to entities, block/tile entities, particles, and even chunks. The result is less RAM, CPU, and GPU usage across the board. The chunk culling is especially impactful, but it's worth noting that it can cause pop-in if you turn really hard really fast.

These are all toggleable and configurable in the mod's config or with a lightweight popup menu in-game which is bound to R by default.

Do note that this can sometimes cause crashes, especially when used with other mods that affect rendering pipelines. It does seem to behave with overlapping culling mods, though, like EntityCulling. On 1.20.1, Revived fixes a bunch of hard-to-diagnose crashes caused by the original.

This is also generally a drag'n'drop you can add to any modpack. Probably.