Debian 11: Program says "Cannot start the Systemback graphical user interface! Unable to get root permissions."

[nokel]

launching with pkexec asks for root password then crashes with
"qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb."

You CAN get it to work by typing the following into terminal on the desktop manually:

xhost +local:
sudo su -
export DISPLAY=:0.0
systemback

but trying to make that into a bash script to automate it doesn't seem to work...