I occasionally have to redo this when monitors get reset or something:
It's a little similar to the others' answers that suggests xrandr. Run:
xrandr
This should output something similar to my dual monitors setup:
Screen 0: minimum 16 x 16, current 4920 x 2160, maximum 32767 x 32767
XWAYLAND37 connected 1080x1920+0+0 (normal left inverted right x axis y axis) 270mm x 480mm
1080x1920 59.96*+
XWAYLAND38 connected 3840x2160+1080+0 (normal left inverted right x axis y axis) 700mm x 390mm
3840x2160 59.98*+
Steam currently launches on the smaller screen and I want to use the 2nd larger screen, in this example called XWAYLAND38
. So I need to mark that as the primary (again).
xrandr --output XWAYLAND38 --primary
If you launch xrandr
again:
Screen 0: minimum 16 x 16, current 4920 x 2160, maximum 32767 x 32767
XWAYLAND37 connected 1080x1920+0+0 (normal left inverted right x axis y axis) 270mm x 480mm
1080x1920 59.96*+
XWAYLAND38 connected primary 3840x2160+1080+0 (normal left inverted right x axis y axis) 700mm x 390mm
3840x2160 59.98*+
The correct monitor is now marked as primary and games should launch on it.