It seems to be in testing right now before a larger roll out but if your account is eligible, you'll be prompted on the sign in page to create one like I was today.
Here's the security screen showing the new passkey.
The passkey has no 2FA tied to it at this point. Hopefully that's coming as an option although both Apple and Google have pretty good security practices with syncing passkeys as using them requires biometrics or your device PIN in addition to compromising those accounts.
I've grown to really like the convenience of using my fingerprint on my Mac or my Face ID on my phone to log into sites where I have set them up. I won't do it for my primary bank account just out of an abundance of caution but I've been adding passkeys for other sites to my iCloud keychain.