That would be possible on a mastadon/fediverse server.
Discussion
What makes you say it’s possible there and not on Nostr?
The benefit of Nostr in my opinion is the frictionless sign up. Password management is so terrifically bad that keys would be a relief for most
Nostr, by it's nature, won't hide post. It's design is to make everything except DMs public.
For right now (afaik) your nostr option would be to have a private chat group that you all share to keep posts private.
It's a very recent addition, so I don't know all the ins and outs of that setup yet.
idk, maybe that would be close enough?
I'm also not sure if any clients besides Amethys support it yet.
Private posts are completely possible on nostr.
The author of the private post would keep a list of people (call it their “circle” maybe), and they share a decryption key with everyone on this list.
There just hasn’t been an NIP describing an ideal flow yet
Sounds pretty close to NIP 24 maybe?
https://github.com/nostr-protocol/nips/pull/686
That's the group chat I mentioned.
NIP 87 is also being worked on for larger groups.