How can we use Passkeys WITHOUT turning on iCloud Keychain?

Why are we forced to sync passkeys when we don't want passkeys shared across our devices?

Merits of Apple's encryption aside, many of us have vested interest in NOT sharing content between devices. I do not want a passkey created on an iPhone shared w/my iPad at home for example. Make matters worse, Apple does not let us select WHICH passwords (or passkeys) to share online. So if you store passwords, for example, in keychain that you will never use on a mobile device, well you have no choice it will be shared w/your phone if you want to use the same profile on both devices. Apple used to stand for privacy and choice, but these days it is more just privacy (sort of.)

So how can we use passkeys without have said passkeys shared across our other devices?

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Given the all-or-nothing force-fed iCloud Keychain for HomeKit, we ended up having to create a dedicated Apple ID just for the home network so we could keep the real passwords from getting synced to different places.