I used to work for a well known communication app, the kind everyone here used. Couple things I learnt about "end to end encryption":

- You can call your service e2e encrypted even if every client has the same key bundled into the binary, and rotate it from time to time when it's reversed.

- You can call your service e2e encrypted even if you have a server that stores and pushes client keys. That is how you could access your message history on multiple devices.

- You can call your service e2e encrypted and just retrieve or push client keys at will whenever you get a government request.