Disable laptop screen and use only VGA

Run the command xrandr -q to shows the exact names.

xrandr -q | grep 'VGA\|HDMI\|DP\|LVDS'

This is a sample command to turn off LVDS-1 and enable VGA-1:

xrandr --output LVDS-1 --off --output VGA-1 --auto

To switch back:

xrandr --output VGA-1 --off --output LVDS-1 --auto