Imagine a password, but it a) types itself for you and b) detects when it's being sent to an impostor site and blocks them from seeing itself, so it can't be phished.
Tada, passkeys.
Cool, where are they stored? (I know the answer: 'it depends', and that's the big problem with their usability: most users haven't a clue what the answer is and most tech support can't answer that question straightforwardly because it depends on some decisions the user probably didn't even realise they made).
As others have pointed out, this is a terrible oversimplification which misses all the nuances which cause people headaches when using passkeys.
To your point, I for example would add point c) - Is linked to the device you are using currently. If you want to use another device to log in you are in a world of complexity and pain.