No… you can also sync with iCloud Passwords, or use a hardware token, like a Yubikey.
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...