Passkeys is the "normal" name for a FIDO2/WebAuthn credential that basically lives within a phone or password manager. It does add a few things. Namely the ability to store many passkeys per device per app/site, the ability to sync those passkeys (e.g. via iCloud or similar), and the ability to use QR codes and Bluetooth to do a local-only authentication on a device which doesn't have the passkey (which is what often requires some proprietary implementation).

This[0] is a good podcast to listen to with Adam Langley from Google about how Chrome supports Passkeys and why they're a good thing. It includes the details of how/where/why there are some proprietary bits needed to implement "Passkeys".

[0]: https://securitycryptographywhatever.buzzsprout.com/1822302/...

FIDO Alliance Press Release https://fidoalliance.org/apple-google-and-microsoft-commit-t...

Chromium Blog on Passkey support (Dec 8, 22) https://blog.chromium.org/2022/12/introducing-passkeys-in-ch...