> Since Telegram isn't end-to-end encrypted they do have a private key that decrypts all the messages, since they only encrypt in transit E2E encryption refers

> Since Telegram isn't end-to-end encrypted they do have a private key that decrypts all the messages, since they only encrypt in transit E2E encryption refers to transit encryption. The encryption is between two end devices, rather than decrypted (and re-encrypted) between clients and servers. It has no bearing on data stored at rest on the end device, and I have no idea what either WhatsApp, Signal or Telegram does to the data at rest.