I am not talking about post processing settings I want to make my own effect.
How can I put a shader into the final rendering pass?
What kind of effect are you trying to achieve? We need more information to be able to help.
5 days later
I would like to make a hallucination effect. At certain times of course.
Define 'hallucination effect'
Like wavy lines on the screen
You probably want a shader setup like described in this page of the documentation: https://docs.godotengine.org/en/stable/tutorials/shaders/advanced_postprocessing.html