This is a work in progress.
Layers 22 to 31 are free to be used by world creators. The name of the layers cannot be changed, so the Unity project settings are ignored.
Layer 22 is often used for PostProcessing, but you don't have to.
Layers can be divided into groups that share the same settings.
When working with Udon, the layer names of the project are ignored, and will be different in-Editor than in VRChat.
You should use the layer index instead.