> If you don't want end-to-end messages made available to others, set your notifications to only show that you have a message, not what it contains or who its from.

Why would an encrypted app broadcast your messages to notifications? That sounds like a failure of the messenger service vendor to secure their app. My banking app requires me to log in to read messages and my account statement EVERY TIME. I get a notification that is just that, notifies me of some pending information, not the information itself.