Replaces the background of the main menu with a custom shader, which can be customized.
This is a port of mat's Menu Shaders mod.
To customize the shader, create a file named menu-shader.fsh in your Resources folder with the shader you want.
For a few already made shaders, checkout this Twitter X thread.
If you want to convert shaders from shadertoy yourself you can try using Tning's Shadertoy porter, but be aware that not every shader will work.