[jeroenhd]

That's true, but I don't think GDM actually cares about OpenSSH.

On my machine (which I didn't alter from Ubuntu defaults) GDM runs after:

    system.slice switcheroo-control.service dbus.socket plymouth-quit.service console-setup.service cloud-config.service gpu-manager.service rc-local.service systemd-journald.socket systemd-user-sessions.service basic.target plymouth-start.service [e-mail] fwupd.service sysinit.target

according to systemctl show gdm.service --property=After

cloud-config is the weirdest one, but it has to do with locales and system configurations for automatically deployed systems (and after first install), I believe. [e-mail] is also strange, but doesn't even show up in systemd-analyze blame.

In my boot-analyze charts I don't really see that many problems with illogical start orders to be honest. systemd-networkd-wait-online seems to hold up a bunch of networking services but that depends on the rest of my network responding in time so I can't even blame it for that.