Some people are working on private, e2ee DMs and group chats for nostr. I would generally say that beyond a certain size, a group chat has to be assumed to be compromised, so using it with encryption is almost not desired as it gives a false sense of privacy.

Nostr being a successful DM protocol was not on my BINGO card but it might be necessary in the light of Telegram, WhatsApp and maybe Signal all being compromised and not private with the meta data to begin with.