It seems to be possible to do local notifications (notifications triggered by the app itself without using a server), but I don’t know if I will still need to setup the complete Push Notifications system for Android and Apple in order for local notifications to work?
Not sure if it’s still the case, but back in the day on iOS, if your app was in focus while a local notification would be triggered, the notification wouldn’t be shown to the user (your app’s code would get a message though)