I was confused also, I use my Yubikey a passkey, so I did not get the rant.
Yubikeys can be used as a device-bound passkey, that the FIDO2 thing.
Now software managed passkeys are also a thing and can be stored in a (good?) old password manager, of course this is less secure and could be disallowed in the future.
Thus the rant is about people without dedicated hardware keys that would have to use things like device-bound passkeys their OS instead of their password manager.
Yubikeys can be used as a device-bound passkey, that the FIDO2 thing.
Now software managed passkeys are also a thing and can be stored in a (good?) old password manager, of course this is less secure and could be disallowed in the future.
Thus the rant is about people without dedicated hardware keys that would have to use things like device-bound passkeys their OS instead of their password manager.