Xamarin local notifications set to low importance still risk audible alerts on some devices

Goal

I want a Xamarin app (Android and iOS) to post local notifications that appear silently in the shade or Notification Center, with no sound, vibration, banner, or badge. The design intent is a low-priority status update that the user can check at their convenience.

Constraints and uncertainty

On Android, the plan is a NotificationChannel with importance set to Low or Min. On iOS, the plan is delivery with UNNotificationPresentationOption.None so the alert lands only in Notification Center. Both platforms require notification permission first (POST_NOTIFICATIONS on Android 13+, alert authorization on iOS).

The unresolved concern is reliability across devices. Research suggests some Android OEM skins (for example MIUI or EMUI) can override channel importance, and on iOS the outcome may depend on which authorization options were originally requested and how the user has configured Settings → Notifications for the app. Emulator testing may not reflect real device behavior.

Questions

• Is channel importance the only reliable control for silencing Android notifications, or must sound and vibration also be disabled explicitly on the channel to survive OEM overrides?
• On iOS, does requesting alert authorization at first launch make truly silent delivery impossible later, or can presentation options still suppress sound and banners per notification?
• What is a practical way to verify silent behavior on physical devices without relying on emulator results?