yeah but I don't use desktop clients or web clients

yes I don't want amber, an application, running in the background feels like a workaround (it is)

what I don't get it

On android, you can replace the launcher (desktop,application list, etc) with custom launchers. What if PosterChan , see https://poster.place, could replace your phone launcher with a nostr-native experiuence? it already does calendar, email, nostr, notes, password and bookmark sync, password autofill, and more... Then....you get what you want a nostr signer built in the phone