XMPP; an open protocol that can be as basic as IRC or extended to support everything Telegram does and more. Decentralised (since it’s a protocol), and E2EE through OMEMO or by encrypting with PGP client side is something your provider can’t even have control over.
XMPP with the OMEMO extension is close, no? While Matrix isn’t distributed, it is decentralised like Lemmy and Mastodon, and E2EE by default. That could be the closest thing to what you mean?