I've set up a few passkeys to see what it's like and the experience is wildly different between sites.

State Farm is the only place I've actually liked it. I don't have to type ANYTHING in.

Open browser, open password manager, click the "sign in with existing passkey", browser and password manager talk, prompt me to confirm the passkey choice, and I'm in.

Most sites I've messed with insist on you entering a username first.