xrandr offers powerful screen management capabilities. You can slice single monitor into several virtual screens. Below script is used to split single 4k screen into 3:
+----+----+
| ~1 | |
+----+ ~3 |
| ~2 | |
+----+----+
Save this to virtmon.sh and use it to toggle between virtual screen and original 4k.
#!/bin/sh
if [ -z "$(xrandr --listactivemonitors | grep 'DisplayPort-2~1')" ]; then
xrandr --setmonitor DisplayPort-2~1 1920/470x1080/264+0+0 DisplayPort-2
xrandr --setmonitor DisplayPort-2~2 1920/470x1080/264+0+1080 none
xrandr --setmonitor DisplayPort-2~3 1920/470x2160/264+1920+0 none
xrandr --fb 3840x2160
else
xrandr --delmonitor DisplayPort-2~1
xrandr --delmonitor DisplayPort-2~2
xrandr --delmonitor DisplayPort-2~3
fi