Custom Notifications/Vibration and Running in Background

Hi, I would like to build a smaller app for myself where I can create reminders or tasks from the watch.
However, I read that it is not very easy to allow the app to continuously run in the background and then spit out a pop-up notification and vibrate at a certain predefined point in time. However, the post I found relating to it was over 8 years old.

Does anyone know if such thing would be possible today?

Thanks