The question here is not about the services on the system. But the settings of systemd itself.
Which service to auto-start at boot? Which one don't?
I tried looking around my system, and using internet search but as one might suspect, this is not a simple thing to word in Google.
systemctl
is the command. See for instance https://askubuntu.com/questions/795226/how-to-list-all-enabled-services-from-systemctl – Rinzwind Sep 23 '19 at 18:28