Miziziziz | How to make a mirror in Godot @Miziziziz | Uploaded January 2019 | Updated October 2024, 3 minutes ago.
scripts:
Camera: pastebin.com/Wew088KX
Mirror Cam: pastebin.com/Cf81Kt4u
Mirror Shader: pastebin.com/C7NZJj8p

looks like clipping planes might be added in 3.2, possibly even in-engine planar reflections: github.com/godotengine/godot/issues/3499