Yes same local network only, but it is E2EE - it is really only remote access from the desktop app, to use the mobile app profile. The desktop app has its own profile so there is no merging of those two. SimpleX is not trying to have a connect everywhere slick cloud service - it is very much about security over convenience.

Nostr does have a measure more convenience (shared profile) and i would not say Nostr is actually less secure. It is more that SimpleX aims to only be an instant chat messenger, whereas that is not the primary aim of Nostr at all.