how to run an interactive gui program from another user on debian 12

linux-gui-user-sandbox-demo.sh

#!/bin/bash
# by: Cody Kochmann
# how to run an interactive gui program from another user on debian 12
# inspired by https://gist.github.com/kasunbg/5502cb630429819d07b5dc0cfa26813c

export NEW_USER_NAME=cody-facebook

#---------------------------------
# step 1 - create a new user
#---------------------------------
# switch to root
su
	# create the new user
	useradd -d "/home/${NEW_USER_NAME}" -m "$NEW_USER_NAME"
	# set the users unique password
	passwd "$NEW_USER_NAME"
	# add the new user to the access control list for displays
	xhost "+SI:localuser:${NEW_USER_NAME}"
	# add the user to the sound group so they gui apps can use sound
	usermod -G audio -a "${NEW_USER_NAME}"
# exit root user session
exit

#---------------------------------
# step 2 - record the display id
#---------------------------------
# record the value for $DISPLAY
echo $DISPLAY | tee /tmp/display.id

#--------------------------------------------------------
# step 3 - now the new user can launch gui applications
#--------------------------------------------------------
# switch to new user
su - "$NEW_USER_NAME"
	# load the display value
	export DISPLAY=$(cat /tmp/display.id | grep .)
	# now the $NEW_USER_NAME can startup gui programs while the og user is still signed in
	firefox