I've noticed that after installing of Cloudron on Ubuntu 20.04 there was an X-server and gnome-shell running. That happens because of a package dependency (collectd -> libnotify4 -> gnome-shell).
It can be prevented by installing libnotify4 before one installs Cloudron:
apt install libnotify4 --no-install-recommends
This error is also present in the DigitalOcean marketplace image.