Looks like the OP tried to simplify things, but I think he's takes it too far. No mention of how FIDO preserves privacy, or how WebAuthn works with the browser protect against phishing. It doesn't get much beyond saying it's a protocol based on a public / private key pair.

Perhaps that is fair enough because his problem seems to be on how that private / public key pair is managed, as evidenced by his comment at the end:"I am waiting for an open solution that will give me the authority to manage and sync passkeys". But if you make Joe Citizen responsible for the protection of the private key, you will end up with plain text copies of it everywhere. That doesn't look like a workable solution to me - it's barely better than passwords.

WebAuthn went to the other extreme - it seemed to built on assumption the private key was stored in a hardware token and could not be copied. But that meant your ID died when the token was lost or broke. In effect in WebAuthn the private key was so well protected it also wasn't a workable solution. (Actually, they had a published solution to the lost token problem - you kept multiple tokens, and authenticated with every site with all of them. I don't know why they though that was going to fly.)

Passkey is somewhere between those two extremes - companies with a track record in protecting private data keep a copy, and manage the transfer between secure repositories. It's a step down in security, because you how have to trust the company not to leak it. But to be fair, I'd trust Google's ability to keep it secure more than I'd trust myself. You also have to trust the company to not give copies to devices that could leak it. So far they only seem to be trusting phones they make, which is a big restriction but is understandable. I can live with those compromises.

I'm not so OK with "if Google deletes my account, I lose my key". They are talking of allowing the transfer of the private key to other companies. Google giving a copy Apple is an obvious example, as it would lets you transfer your ID from Android to iOS. But so far it's only talk. And if they continue to insist only a phone they control can be trusted to store the key then even if they do allow transfer it still leaves you with just two key minding providers - Apple and Google.

I don't know what to do about that. You can't trust any machine that lets the user have sudo access (or in general change the software) - so Windows and the traditional Linux desktop is out. (Obviously Linux itself and open source in general is fine - Android is Linux after all. The issue is Linux desktops give their users sudo and then by extension any malware that gets in the ability to change/access anything - including the private key.) Perhaps they might allow transfer to other dedicated tokens. A totally open source token that doesn't support firmware upgrades would work.

In any case the key management problem is complex. Damned complex. The "just make the user responsible for key management" throw away at the end of the OP is never going to fly. It's a simple solution to a complex problem - and it's wrong. The reason we are in this mess state now isn't because Google/Apple are trying to lock you in - it's because there are trying to provide something that works for most people, and there are no easy/fast easy solutions.