I don’t think so unless you trust everyone on the private relay to never broadcast your notes to public relays
Discussion
That’s a fucking shame because it would make this experience 10x better (for me at least)
You can create a private group chat on nostr:npub1tm99pgz2lth724jeld6gzz6zv48zy6xp4n9xu5uqrwvx9km54qaqkkxn72 and all notes in the chat get encrypted, but I don’t think many clients support this.