Um. If you're setting an alarm in the built-in clock app, it definitely works when Do Not Disturb is turned on.
So, I don’t really know what’s going on, then. But unless vibrate and DND is turned off and the volume is all the way up, sometimes the alarm just doesn’t work and I have missed stuff before.
Android was really clear about this: there was just “no notifications”, “alarm only” and “all notifications”. I wish Apple would make a three state toggle like this and bundle it all together ..
(I understand that you’re trying to tell me that alarm should be working, but it just isn’t).
They fix is to reboot the phone.
I cannot trust it for critical alarms, so a simple device by the bed is required again.