How to get a systemd timer out of n/a status?

You must start the .timer unit in order to schedule it – just like you must start .service units in order to make the associated daemon run. Your post shows neither systemctl start, nor systemctl enable --now, nor any other commands which would queue a start job.

systemctl daemon-reload will not automatically start any newly added dependencies for units which are already running (such as timers.target in this case) – the symlink that 'systemctl enable' created will only really take effect on next boot, or if you somehow manually restart timers.target.

I've had this problem and I noticed that the corresponding service was hanging and its status was activating (start). For this reason it was not triggered.

I stopped the service and then the timer showed the next trigger time as expected. Perhaps some people saying that a reboot helped them actually had the same problem.