Virtual Screen handler for expand your desktop to old laptops or Tablets. More info: https://hpsaturn.com/old-laptop-like-second-monitor/

virtual_screen_start

#!/bin/bash

# Secondary display resolution
W=1920       # Virtual display width
H=1080       # Virtual display height

# Primary display config
P="HDMI-A-0"        #is the main screen, it can be calle eDP-1 or eDP1 depending on the driver
O="DisplayPort-0"   #can be a virtual (recommended if possible) or real output accepted by the xog driver.
                    #more info: https://wiki.archlinux.org/title/Extreme_Multihead#VNC

############# END SETUP ##############################################################
PW=`xrandr --current | egrep '\*' | awk '{print $1;}' | cut -d x -f 1 | head -n 1`

# Create the virtual display
gtf $W $H 120 | sed '3q;d' | sed 's/Modeline//g' | xargs xrandr --newmode
gtf $W $H 120 | sed '3q;d' | sed 's/Modeline//g' | awk '{print $1;}' | sed 's/^.\(.*\).$/\1/' | xargs xrandr --addmode $O
gtf $W $H 120 | sed '3q;d' | sed 's/Modeline//g' | awk '{print $1;}' | sed 's/^.\(.*\).$/\1/' | xargs xrandr --output $O --right-of $P --mode
sleep 1

# Android device init
# Forward the VNC port to your device and start a VNC session
# adb reverse tcp:5900 tcp:5900 # uncomment for Android secondary display
echo "Starting VNC server"
x11vnc -display :0 -clip ${W}x${H}+${PW}+0 -repeat -forever -nonap -multiptr -noxfixes

# When cancel this script, turn off the virtual display
xrandr --output ${O} --off

# On the old laptop please run:
# vncviewer -shared -ViewOnly -Fullscreen <host ip>

It's a variant of the Android Display Script script from @8bitbuddhist

This script is workaround to NVIDIA issue with "virtual setup" on X Org for old laptops (the original script was for Android). And also fix some issues in the detection of primary device resolution.