How to use "use_fixed_fit_projection" together with a movable camera?

Thank you very much. It works and I think that I understand it.

I have one more question regarding the rendering. How would I achieve a fixed resolution and aspect ratio that resizes to the current display size but with black borders at top/bottom or the sides. let’s say in the game.project settings I set the resolution to width 720 and height 1280. and then I render this game on a modern mobile device there should be black borders at to top and bottom because the screen is taller.