How to do in Godot the same approach that I do in my games that is show a background/texture moving for entire screen but the game run on safe area or in the game area that is generally smaller than full window available?
The moving background (purple part) is to don’t show that black border.
You will need to disable the project settings that force such an aspect ratio/resizing.
If you are going for a pixel-art style you can use a subviewport to render the game and some UI nodes to render the sub viewport container in the center of the screen, with anything else in the background. If you want to match the screen’s resolution, be it 3D or a high quality 2D game then you may want to use a CanvasLayer on top of everything and cut through your background leaving a gap for the gameplay.