Confusion for private keys

[HakooDesai]

In general, I understood that during registration ceremony, Authenticator generates the Pub/Private key pair, stores a private key and provides public key in response. Now my question is, what happens if Authenticator doesn't store the Private key, i.e. supports residential keys = false?

Also, does Authenticator generates the pair every time it registers with new website?

Can I use same authenticator for same website for multiple usernames?

[timcappalli]

what happens if Authenticator doesn't store the Private key, i.e. supports residential keys = false?

If you request a passkey correctly in the create call, the authenticator will only create a passkey (you can confirm in the credProps response).

Also, does Authenticator generates the pair every time it registers with new website?

Yes, passkeys are unique per RP ID, by design.

Can I use same authenticator for same website for multiple usernames?

Yes. Each passkey is in an authenticator is unique per user account + RP ID combo.