Comment by OneDeuxTriSeiGo

Currently atproto is still figuring out how to approach private data. Right now there exists extremely limited abilities to store private data via the bluesky preferences but until that mechanism is standardised in a way other projects can use, there's not really a good way to store data privately let alone transmit data privately.

There's a working group for doing this but it'll be a while before anything is adopted at scale.

If fully public is okay for you, there is actually already a chatroom/IRC-esque platform called Roomy. It works well but it is all public and there's a touch more latency than a normal client-server platform due to the nature of atproto's gossip protocol.