Yes. You go an add secondary passkey when logged in on another device. Or with another tubikey.

But not all setups support this. Some only allow one. Obvious issues abound.

> But not all setups support this. Some only allow one. Obvious issues abound.

I'd go as far as to say "most setups don't support this. Most only allow one".

The services I've seen so far that support multiple passkeys are in the minority.

Passkeys and u2f keys aren't the same. Systems must support multiple passkeys, otherwise you could only access the service from a single device, since passkeys are usually tied to a particular piece of hardware.

Nevertheless, nothing forces my banking app to accept a second PassKey other than the one linked to FaceID. When I buy a new phone, I need to re-bootstrap auth from zero. There’s no way to store two.

Is the app the only way you interface with your bank? It doesn't have a website?

All of the things I've used passkeys on support both web and mobile auth, which necessitates two keys.

You'd be surprised! There are plenty of new banks in Asia which only have mobile apps. You can't access your account using a web browser at all. They don't even give you a passbook, all banking activity from signup are done via the mobile app.

The majority of sites I've used that supported U2F/passkeys/yubikeys/webauthn support multiple. In fact the vast majority I've used supported multiple, only a few outliers only supported one.

I can't stand services that only support a single U2F key (cough AWS cough)