>>106296929
there's a few ways to do this, for example you could 2x scale your desktop. i assume you're using 1080p given you're asking for a 2x scale
xrandr --output

--scale-from 960x540 --filter nearest
this will set your framebuffer to 960x540 with nearest/point filtering without changing the actual display mode (no custom mode needed)
another option is gamescope, which has settings to do exactly this, especially useful if you want it "full screen" (i.e. centered and surrounded by black) and also not changing how other programs look
gamescope --nested-width 640 --nested-heigh 480 --scaler integer --max-scale 2 --filter pixel --