Windows 11 notification banners not showing?

In Settings → System → Notifications, confirm that Notifications is on. Under Notifications from apps and other senders, select the affected app. Turn on its notifications and Show notification banners. For the next test, keep Show notifications in notification center enabled too, so you can compare what Windows lists with what appeared on screen.

Expand Turn on do not disturb automatically on the same settings page. Check the rule that fits when banners disappear, such as a schedule, a duplicated display, a game or a full-screen app. A Focus session can also turn it on. If you want to keep quiet hours, use Set priority notifications to allow the app you need.

Use a new event you can recognize, such as a message sent from another device, and check whether it appears as a banner and in Notification Center. If other apps work but this sender appears in neither place, check its own notification settings. For a website alert, check the browser’s site permission as well. Old alerts in the center do not confirm that the new test worked.