I don't like the idea of passkeys if they cannot be backed-up or are non-portable locked away in a walled garden and possibly on stored on some corporate cloud

I don't like the idea of passkeys if they cannot be backed-up or are non-portable locked away in a walled garden and possibly on stored on some corporate cloud in some unknown manner. When they can be backed-up, are portable, and have an explicit security policy, then I'll consider them. For example, Bitwarden is able to act as a passkey provider on iOS and can store the passkey secret key gunk into a password record. I tried it out on a couple of minor services that have username & password login alternatives.