So... you need to carry two electronic devices for this so-called security solution?
iCloud Passwords don't run on an iPhone that is an electronic device that you need to carry?
Those electronic devices that you mention don't each store the keys in a proprietary format and you can't access them without the vendor's cooperation - i.e. vendor lock in?
Passkey portability is being worked on. Here is the draft of the open standard:
https://github.com/fido-alliance/credential-exchange-feedbac...
News article: https://www.theverge.com/2024/10/15/24270875/password-manage...