That
is a hopelessly unusable workflow which is why the
default behavior on iOS is storing Passkeys in iCloud Passwords and having cloud sync between devices and cloud backup/restore.
On Windows you can use Apple's iCloud Passwords app for Passkeys now directly, in supported browsers because for whatever reason Apple's engineers didn't want to build a Windows plugin for it (yet?) or you can use the Bluetooth option. Windows 11 makes it very easy to use the Bluetooth option and for better/worse some of the requirements that made Windows 11 stop supporting older hardware were also those making sure that Bluetooth LTE is reliable especially for Passkeys.
In the Bluetooth flow the "only" user facing mediation step is the QR code. Some of Microsoft, Apple, and Google's finest all worked together to make sure that UX is about as simple as it can be with just about no learning curve. If someone is used to pulling up a QR code in the camera app and clicking the default app it wants to pop up, "it just works".
If you hear Bluetooth and think of complex pairing dances, that is nothing like how Passkey signings over Bluetooth work. The devices don't need to be "joined" or "paired", they just need clear enough radios for a quick couple of messages, which a QR code kicks off.