Under the new Wayland display server, several applications requiring root permission fail to run. I actually have an answer (one way of working around the issue). I welcome any better solutions or criticisms.
Many other answers to this issue recommend adding root to xhost which, while it solves the issue, breaks the Wayland security model a bit. It is much better that we add root to xhost only for the duration of the running of the program, be it synaptic or gparted or whichever.
Edit your gufw.desktop file (/usr/share/applications/gufw.desktop in Debian 10) and change the line:
Exec=sh -c "xhost +si:localuser:root && gufw && xhost -si:localuser:root"
Inspired by the post at: https://discourse.ubuntu.com/t/adding-applications-to-start-up/9288 Edit /usr/bin/synaptic-pkexec to comment out the zenity warning message (assuming Debian 10) and change the line:
exec "/usr/sbin/synaptic" "$@"
xhost +si:localuser:root pkexec "/usr/sbin/synaptic" "$@" xhost -si:localuser:root
I imagine other programs can mostly be adapted in the same way as gufw. This does not solve the underlying issue of old programs running everything including GUI as root but at least they can function like before.