E2E in Matrix "works" with which Matrix clients? The whole point of a decentralized federated messaging protocol is to allow people to build their own clients. Do Matrix clients uniformly and interoperably support E2E today?
Nearly; we’re aiming to force on E2E by default at end of Jan (but it’s getting tight). There are at least 6 complete independent implementations, and once cross-signing lands it’s good to go. For clients/bots/bridges without E2E we have pantalaimon (a clientside daemon which you proxy all the traffic through in order to encrypt it).