you either can remember all your passwords and then you are fucked or you use a pass manager

passkeys will be stored in a pass manager and they can be recovered with device pin and master pass, I think they will be exportable too

so yes, you can log in with brain stored stuff

I guess you need a device to log in? then you log in to your pass manager and you can log in to anywhere

only this way you have to remember a passcode and a master pass, not 1000 passwords and you need your master pass 5x/10 years and your passcode every other day and you log in with your device and your biometrics

passkeys have issues but what you are saying is pure shit