Passkeys are such a great idea that is for sure going to be ruined by implementers clinging stupidly hard to their “secure enclaves” making them a huge PITA to actually use.

It should be as simple as storing your private keys in your password manager, browser keychain, in a folder, or USB stick, Yubikey, or anywhere the user damn well pleases.

You should be able to easily export presigned tickets for recovery, support CA style auth for advanced users, and support passcode challenges (ie site gives you a short code you type in and your vault spits out a code) for cases where getting the two devices to talk directly is hard.