Huh? Do you not understand how this works?

So passkey is saved to my account. Account is logged in on multiple devices, secured with an additional pin.

It doesn't matter what device I'm on, I can either use the app on a mobile device or a browser.

Site goes to login, prompts me for passkey, I type in PIN and select the passkey from my password manager.

It's fast and easy to use.

If I am on a random device (which never happens, ever) I would just log in via browser, or use one of my hardware tokens if I were expecting to access something from an unusual device.