What are passkeys?
Discussion
https://developer.apple.com/passkeys/
https://developers.google.com/identity/passkeys
https://blog.google/technology/safety-security/the-beginning-of-the-end-of-the-password/
So a private key is stored locally on device and the corresponding public key is stored in the server.
That’s pretty much just Nostr sign-in.
The only difference is that passkey approach generates a new key for every app. It’s like using a different private key for every nostr client.
They’re login tokens that are encrypted on your device and tied to a master identity.