Is there something like this on top of nostr too? I'd much rather see nostr because it's truly open.
PS: I'm not sure if Nostr has this but bluesky currently doesn't.
There is an E2EE messaging system that works with atproto DIDs, based on MLS, called "germ". People who have accounts can have them associated with the Bluesky profile for easy association. They only had a iOS app last I heard, so most people cannot use it.