Why? I think Google suggests that you send the payload encrypted through the notification. Google then only knows which app to send the message to, they don't know from whom the message originates (only "a Telegram server") nor what the content is.

Also, you could just send a notification instructing the app to fetch a new message from your server.

From the docs:

Encryption for data messages

The Android Transport Layer (see FCM architecture) uses point-to-point encryption. Depending on your needs, you may decide to add end-to-end encryption to data messages. FCM does not provide an end-to-end solution. However, there are external solutions available such as Capillary or DTLS.

https://firebase.google.com/docs/cloud-messaging/concept-opt...