Comment 5 for bug 1713311

Generally speaking, all (Wayland-capable) apps that currently run their UI as root need to be restructured to use PolicyKit for the privileged operations, and have the UI run as a normal user.

Apps that do not run on Wayland and use the legacy Xwayland compat, but you need to run xhost +si:localuser:root first. gksu is apparently broken because it assumes that there is an Xauthority file, but that's not the case with XWayland (I'd assume it would work with pkexec, for apps registered with PolicyKit, as a temporary workaround).