There are 2 installation methods:

Optifine(for Forge, or without modloader) and Optifine alternative(for Forge, Fabric, Quilt)

Note: From v1.3.4(for Minecraft ver1.21.4), file name has [Opti](for Optifine) or [EMF](for Optifine alternative) or both of them. You can notice what which mod can use CMMRP from file name.

How to Install (Optifine version)

How to Install (Optifine alternatives version)

Written by Rokuyon Shirotamaya