4.6.3
How do I make my game scale to the size of the screen when in fullscreen mode? I followed the instructions here for pixel art games, but when my friend tries to play in fullscreen, the game is too zoomed in. It’s also too zoomed out on my screen, although that’s much less of an issue. My window settings are here.
Is your game 2D or 3D?
Also might be worth to try Godot’s demo for resolution in action 
Multiple Resolutions and Aspect Ratios Demo - Godot Asset Library
But generally for viewport in window mode you can change resolution via code.
For fullscreen it will behave differently as it takes system resolution of monitor( on Mac for example it’s always monitor highest resolution, on Windows it should be your system settings/graphic driver setting)
Change scale mode from “integer” to “fractional”.
See if that helps.
