I think to have a Nostr private group chat need to setup a private relay. Doesn't need to be paid just private. Then there could be a group chat that wouldn't necessarily leak to everything. nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955 would need to add the "post to specific relays" feature first tho. Just thinking out loud.