VRChat has always had a rough time with sorting and or blending see-through objects, which is more complex to calculate for compared to any solid geometry. This isn't helped by the fact that the textures holding your screen aren't cleared at the end of each frame. Usually this is not a problem because the skybox is rendered before anything else, but leaving transparent stuff on the screen as the next frame renders makes double the work for really no reason at all.
Included in this unitypackage are a couple things:
Disclaimer:
Although I put a fair amount of trust in what I build, If this miraculously breaks or doesn't work, come yell at me in my project discord
You are not required to credit me in your resulting VRChat worlds, just putting my work out there for this one!
All you have to do is import this package into your project, drag "Assets/OwenTheProgrammer/Utils/FrameClear/FrameClear.prefab" into your scene and forget you ever did it.
This package does require udon if you want the mesh to automatically enable itself when building, if you wish to remove udon, simply don't forget to turn the mesh back on when you push your world to VRChat.