Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won’t work on another device.
Now I don’t know if that key can be stolen or not, or if it’s really more secure or not, as people have really unsecure pins.
You can protect your passkeys with a knowledge element.
But I don’t see your use case. Passkeys are about logging in to webservices, not about protecting devices.
Web service providers can always be ordered to surrender your data by a court. Very few of them even try to encrypt your data. And for those that do, a court order could still force them to intercept your password and decrypt the data.
If you replace passwords with passkeys that must be protected by a password, you haven’t replaced passwords, you’ve just moved where the attack can happen. While I think there’s certainly value in that, it’s very disingenuous to say you’ve replaced passwords.
Passkeys are used for more than web services and have the possibility to replace other security options elsewhere (being something you have, one of the three secrets possible). Their lack of protection, at least in the United States, is a very serious problem. Your points do nothing to address this and highlight just how bad the situation is.
You should really read up on multi-factor authentication and Web-Authn.
Your problem seems more that you don’t trust Google to store your private keys in their cloud.
And that’s fine. You don’t have to do that. But don’t be confused to think that’s the only option. You can buy a yubikey or a Trezor model T if you prefer.
Passkeys are just a marketing term for Web-Authn. When you use asymmetric keys for other purposes, it’s not passkeys.
I missed the part where I said I don’t trust Google. You seemed to have ignored everything of substance in my response, namely putting a password on the passkey doesn’t remove passwords and the extension of things like FIDO2 beyond web auth.