Same issue. The metadata is always somewhere. On Signal, the servers at the company know the destination user and the time of the message. They claim to not be saving it, but who knows... For SimpleX, it's similar, but on their relays instead.
Discussion
Hmm was my understanding nostr:npub1exv22uulqnmlluszc4yk92jhs2e5ajcs6mu3t00a6avzjcalj9csm7d828 didn’t know the destination user at all? Not very similar?
To the best of my understanding, that is only true if you use a different IP for each contact of yours. Otherwise, the server can easily bundle your queues and map out who you are. They call re-using IP an "opt-it" security issue. Even though most people are reusing the same IP for everything.