Bash script to use an Android device as a second monitor for Linux. See https://blog.8bitbuddhism.com/2019/12/01/how-to-use-your-android-tablet-as-second-monitor/ for detailed instructions.

create-android-display.sh

#!/bin/bash

# Make sure your Android device is plugged in and accessible over adb.

#### Remember to enable virtual displays in xorg by adding the following to your configuration (e.g. /usr/share/X11/xorg.conf.d/20-virtual.conf)
# Section "Device"
#    Identifier "intelgpu0"
#    Driver "intel"
#    Option "VirtualHeads" "1"
#EndSection
#### If you use AMD or Nvidia, change the Identifier and Driver options to match your GPU.

W=1920      # Virtual display width
H=1080      # Virtual display height
O=VIRTUAL1  # The name of the virtual display (check using xrandr)
P=eDP1      # The name of your physical display (check using xrandr)
PW='$(xrandr --current | grep \* | awk '{print $1;}' | cut -d x -f 1)'

# Create the virtual display
gtf $W $H 60 | sed '3q;d' | sed 's/Modeline//g' | xargs xrandr --newmode
gtf $W $H 60 | sed '3q;d' | sed 's/Modeline//g' | awk '{print $1;}' | sed 's/^.\(.*\).$/\1/' | xargs xrandr --addmode $O
gtf $W $H 60 | sed '3q;d' | sed 's/Modeline//g' | awk '{print $1;}' | sed 's/^.\(.*\).$/\1/' | xargs xrandr --output $O --right-of $P --mode
    
# Forward the VNC port to your device and start a VNC session
adb reverse tcp:5900 tcp:5900
x11vnc -localhost -clip ${W}x${H}+${PW}+0

# When the session ends, turn off the virtual display
xrandr --output $O --off

NVidia driver doesn't support virtual screens. And, mentioned "intel" driver is legacy one, current intel's "modesetting" driver doesn't support virtual screens too. Please, read the following materials for possible solutions: StackExchange: Unable to add a VIRTUAL display to Xorg ArchLinux Wiki: Extreme Multihead

Thanks, this documentation is clear. My driver is amdgpu for this reason I used the modeline alternative. I did a simple a script for old laptops (secondary display). Also I fixed some issues on the resolution detection on the current script:

https://gist.github.com/hpsaturn/7b6d15f149eb5bb9bdb19b94b1b34c42

Also it should be works with Android.