The following information is derived from the plugin description.

Passkeys are a more secure replacement for passwords and are based on industry standards for account authentication. They provide faster and easier sign-ins across a users devices, and are always strong and phishing-resistant.

To sign in with a passkey, the user approves the sign-in with the same biometric or PIN used to unlock their device (such as a phone, computer, or security key). Passkeys can be used in addition to any other authentication method enabled for the server.