I found the option "Allow Hidpi" in project settings -> Display -> Window -> Dpi
What does the settings acutally do?
It says that it only affects Windows and macOS becuase "DPI-awareness fallbacks" are not supported on Linux.
I set the size to 3840 (Width) and 2160 (Height), the maximum resolution I want to support. I set the Test Width to 1920 and the Test Height to 1080, my real resolution (of the pc I am developing the game on). I set the Stretch Mode to 2D and the Aspect to keep, to make the game compatible with other screen sizes (like 21:9, 16:10).
Do Windows and macOS need this Hidpi option to work?
I use Godot 3.2.2 on Ubuntu 18.04.