The MacOS situation has been the most confusing. Neither Safari nor Chrome can use passkeys, which makes me think Apple either doesn't allow/support syncing them directly to the MacOS keychain, or the (windows hello-esque) APIs to access them are just not there.
What I’d expect from Apple is the Passkeys are stored in iCloud Keychain. To use it would ask for Touch ID authentication on that same device, then provide the key to the website after a successful auth.
The “go find your phone and take a picture of this QR code” seems like insanity, even if they’re trying to require two devices to authenticate.
Windows exposes APIs for "windows hello" - which is an easy way for apps to authenticate via usb authenticators or windows' built-in authenticator (when available via TPM). I imagine that, on macOS, such an API would allow apps to authenticate using any passkeys in iCloud Keychain directly, of course with an OS-based user presence requirement like entering system password or using touch ID.
