Comment by wtf_srsly

As far as I know, WhatsApp on iOS uses a special entitlement (com.apple.developer.usernotifications.filtering) for securely handling notifications.

They receive silent push notifications, which wake up the app (a reason for the entitlement being restricted). Once awake, the app takes over, managing the notification itself.

This approach circumvents sending notification content in cleartext through Apple's servers, thereby preserving their end-to-end encryption.