Does this by any chance works against built-in applications that don't allow you to disable notifications?
Last week I was configuring Samsung for my mother and it constantly nags her with notification for setting up Samsung account (that's not the worst offender tho) and frankly that would really help here.
It should be able to, unless they are using Live Update [0] notifications.
[0] https://developer.android.com/develop/ui/views/notifications...