Compositing causes rendering issues with 4.16
Upgrading from Ubuntu 20.10 to 21.04, xfwm4 was updated from 4.15.5 to 4.16.1.
/var/log/dpkg.log:2021-05-06 08:51:21 upgrade xfwm4:ppc64el 4.14.5-1 4.16.1-1
Using X2Go, there are now rendering errors, like screen not updated, shadow around panel, icons not at right place until mouse over.
Disabling Compositing in the Window Manager Tweaks (
xfwm4-tweaks-settings), fixes these issues.
I have no idea, if this is a driver issue, or something xfwm4 should be able to automatically figure out.