Notes on the quest to get the alarm clock to wake up the phone from suspend: this executed as user mobian actually resumed a L5:
systemd-run --collect --user --unit=alarm-clock --on-active="1m" --timer-property=WakeSystem=true gnome-clocks
Resuming without root permissions seems to work now (progress)!
There are still bugs, also saw https://github.com/systemd/systemd/issues/29245
Now, gnome-clocks "just" needs to call the required systemd timers to make the phone wake up on time...