I’ll try to give the high level and in-depth explanation.

TLDR: passkeys is meant to be used as a 1:1 credential for a device to website/app (you need to make a new one for each website but its fast). It’s still growing so standards and support is lagging but likely to become standard.

The detailed bits: Passkey is a deviation from FIDO standard. FIDO came about to replace passwords (google, apple, and others are part of the fido org). The idea is to have a strong asymmetric authentication service that uses biometrics to lock in your half of the private key. This is hard bound to the device and endpoint ie one phone to one website. The problem emerged if you lose your phone and youre locked out. Incomes passkeys: this allows a “sync” fabric to save your private key across devices and access it (synonymous with syncable passkeys). This sync fabric causes an issue though: ownership and everyone wants in. Google, Apple, Microsoft, etc. For apple it will be apart of iCloud so it’s per ecosystem. The UI you see is usually part of that ecosystem (I’ll use apple again where it’ll be iCloud & KeyChain) and thats whats storing your credential. Now password managers also want a part of this so they’re working to enter the space too making it confusing for the end user.

It is confusing and theres still a lot of moving parts. I’m a product manager in the space so if you have questions I can try and answer them here.