instead of copy pasting your nsec everywhere, try to inject your nsecs via.... Amber (Android) nos2x or Alby (Browser extensions) nsec.app (browser app) is there an app for iOS?
npub all day, but careful with that nsec
good question. not sure as I don't have any apple devices.
Bitwarden
There is no native like Amber. There is a browser extension called NoStore but it only works in Safari.