Question:
Android - Show full-screen notification when app is in the background

Based on the documentation for setFullScreenIntent (https://developer.android.com/reference/android/app/Notification.Builder#setFullScreenIntent(android.app.PendingIntent,%20boolean)), full-screen intents are intended for urgent, high-priority notifications such as incoming calls or alarms.

From the related article (https://source.android.com/docs/core/permissions/fsi-limits), there are guidelines on how to use this feature and limitations on its behavior, but the exact behavior can depend on the state of the device (locked /unlocked ...) and system-level restrictions.

Key Considerations:

1. Full-screen intents are designed for notifications that demand the user's immediate attention. Misusing this feature can lead to a poor user experience.
2. It is crucial to provide users an option to disable full-screen notifications and fall back to regular notifications when they are not essential.
3. The documentation indicates that there are limitations on when full-screen intents will be shown, depending on factors like device state, but I do not have firsthand experience with how it behaves under specific conditions.

These are untested notes based on research. While this answer is late for the original poster, I hope it is useful to anyone who encounters this issue in the future.