I don’t get what the issue is — how to use it is explained in the descriptions, just re-read them. In the updated CopperCube Screen Shader Extension, you can now switch cameras without any problems. If you want to use multiple different effects, then yeah, you’ll need to combine them into a single shader and write a callback to switch between the effects.
Viewing post in Old School Screen Shader comments
I have encountered a serious issue where when the game scene restarts, the camera sometimes feels like it's stuck inside something, making it difficult to move and even getting stuck outside the level. More serious games will be closed directly. I am very certain that it is a problem with the shader because when I turned off the shader, my game never had any issues again. If you need it, I can record a video and send it to you