well, these folks invent nostr private messaging.
yet no one seems really using it.
Discussion
Everyone can see who sends messaged to whom, when and how long those messages are. Only the content of the message is encrypted.
Not very private.
still does not forget the fact that peoples are rarely login into someone else pubkey just to see their things like PM list.
It doesn't matter if people choose to use clients that don't display when other users exchange messages. That's just because they aren't interested in seeing when they do.
Anyone can build a client and seeing when other users exchange messages is trivial, so that information is not private at all.
That's because of all the metadata it exposes