The assigned date can be how you want to interpret it, i.e. the created date but also a due date. This is one option.
We don’t offer an explicit due date, but you can use either tags for this (see the due tag section in Tags, Links, and Lists). This is the second option.
Finally, you can of course create a reminder within the note and use that to inform/alert you when the note is due (third option).
We don’t want to support alarms as this belongs in the calendar app (which reminds me, you can also assign a calendar event to a note and set an alarm on that event in the calendar app, option 4), nor note level reminders (as it would confuse users who would now have to pick between a reminder and event linking).
Hope this offers some ideas how to best approach things.