Notifications while outside app

Hi everyone, I want to make an app where when it gets to a specific time set by the user, the app sends a notification. I want this notification to show outside the app. As far as I know, this is only possible using extensions. I am a newbie to MIT App Inventor, so please help me.

Maybe this will help you:

Or maybe there will be someone else who has already implemented this who will explain it to you in more detail, but in the meantime I'll leave you with something to start with.

This is the perfect use case for the alarmmanager extension

Taifun