Yen Chiang Liu, Apologies for the delayed response.
As you have mentioned, we can leverage this' function to fetch the outcome via notificationId but not trackingId : NotificationHubClient.GetNotificationOutcomeDetailsAsync(string notificationId)
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Just to highlight, successful notifications mean simply that push notifications have been delivered to the external PNS (for example, APNs for iOS and macOS or FCM for Android devices). It is the responsibility of the PNS to deliver the notifications to target devices. Typically, the PNS does not expose delivery metrics to third parties.
Please check this Azure doc: What telemetry features are available?
I'm checking on this internally and will post back as soon as I have more updates.