And I can't get my head around passkeys yet. Haven't switched to them. Haven't developed a clear model of where's my private key exactly how many of them and how to get to them if my camera or fingerprint sensor isn't working etc.
It might help your mental model to think about them as identical to hardware security keys. Except now you don't need to buy a specific hardware key, your password manager is it. You can also just use your hardware key as your passkey, same thing (as long as the key supports FIDO2).
Specifically for your question on what happens if you lose face/fingerprint sensor. So this would be assuming you use Android/iOS's password managers, in that case even with biometrics failing you can just use the code you set on your device as both have fallbacks.
Couldn't we just make password managers pretend that they're a Jubikey or similar?
Is it that Jubikeys don't offer any extra (master password / biometric) authn, and hence are only suitable as a second factor, where password managers can be used as both?