How to have my iPhone 11 iOS remind me of upcoming appointments?
Calendar appointments can have alerts.

You can set an alert to be reminded of an event beforehand.

Tap the event, then tap Edit near the top right.

In the event details, tap Alert.

Choose when you want to be reminded.
For example, “At time of event,” “5 minutes before,” or another choice.



https://support.apple.com/guide/iphone/iph3d110f84/ios

Reminders can have due dates. You'll be reminded at the time you choose.


Tap the date and time button  to set a due date for the reminder. Choose from Today, Tomorrow or This Weekend, or tap Date &amp; Time to set your own day and time.

https://support.apple.com/kb/HT205890