I have tried this and it worked well.

At first, I just clicked the start button in app but nothing happened. So I try to snooze the notification for 15 min and after 15 min the notification didn't appear. So is this the right way to use it?

If I want background app notification appear again, what should I do? Just uninstall it?

Device: Pixel, Android 8.0
Version: 0.3

• Permission granted
• Switch to Enable in main activity
• Snooze the notification manually

The app does not snooze the notification as intended to.

Guessing reason:
Maybe cause by notification change, the number of app running in the background becomes 2 from 1, and cause some kind of ID changes, then this app can not snooze it in the next duration. (Not verified, just a hypothesis)

Maybe the app hasn't snooze any notification programmatically.

Device: Pixel, Android 8.0
Version: 0.2 and 0.3

“App is running in the background” and “Drawing over other apps” notifications can now be easily disabled by the user just like any other notification channel: long press the notification, disable the toggle, and you are done!

From https://www.xda-developers.com/android-8-1-oreo-developer-preview-features/

NotificationListenerService only has a snoozeNotification(), but no unsnoozeNotification().
I found it in NotificationAssistantService, but it's a hidden system api. I tried to use reflection to call it but failed.

"Item not found", the link is in readme.md
Store area: US