Created attachment 133287 [details]
script to setup virtual screen

I use xrandr to set up a virtual monitor, which I can then access via VNC on android tablet and use as a second monitor. This can be done over USB for relatively good performance.

Some xorg drivers include natively the possibility to add virtual outputs, for example the old xf86-intel driver and the amd driver. In this case, there is absolutely no problem, Kde detects everything, and one can configure xinerama from systemsettings5.

On the other hand, the moder intel "modesettings" driver and the nvidia driver do not provide this capability. It is still possible to add virtual monitors by adding a modeline with xrandr to a real but disconnected output, i.e. add the monitor as HDMI-2 even though there is nothing plugged into HDMI-2. Otherwise, one can use the evdi driver to add a fake external card.

This works fine, one can export the virtual monitor with any vnc server and one can move windows to it. It also appears correctly in fullscreen screenshots when using xinerama. But the "virtual" monitor will always appear as "disconnected" on xrandr. As a consequence, KDE will not show it in systemsetting5, and not set a desktop background for it (it will stay black).

I've attached a script to set up this virtual monitor. It uses ADB (android debug bridge) to connect via USB, but this is optional and won't be used if ADB is not found. In this can one can simply connect via local network