Maybe?

Encrypted makes the contents of your messages private.

What is public on nostr is metadata like your profile information linked to each note and the date/time and possibly also the message size.

That's nostr.

SimpleX has metadata too, but it uses ephemeral (throw away) identities for every connection which limits the scope of information that it can provide over time. I.e. You can't tell that Bob spoke to Alice _and_ that the _same_ Bob spoke to Carol.

So really simpleX is better e2e encrypted messaging but I haven't read all about simplex yet so I'm going off rhetoric only right now.

Nostr can provide private encrypted data storage which may be useful for allowing you to access your simplex connections across platforms. Maybe this can allow us to make simplex chats feel native to nostr.