Comment 82 for bug 1951491

For those of us who are using Xubuntu, X2Go and experiencing this problem, I have a work-around:

I had already switched firefox to the apt repository version, so I installed the chromium snap to test with. As expected, it failed to launch with the same issue mentioned at the top of this thread:

/user.slice/user-NNN.slice/session-1.scope is not a snap cgroup

So, I added this file:

/etc/x2go/Xsession.d/96dbus-snap-fix

containing:
export DBUS_SESSION_BUS_ADDRESS="unix:path=$XDG_RUNTIME_DIR/bus"

After logging out and back in via X2Go, the Chromium snap worked. It is my hope that this fixes snaps for ALL users without having to edit individual user login files (like .bashrc).

Edit:
I removed the PPA version of Firefox and replaced it with the snap. Working perfectly.