Again, though, that's beside the point. If you want a system that provides that, use one. You aren't locked in to any single company. It's an open standard.
Again. No system that I know about provides those properties today, so your "use one" advice is, unfortunately, impossible at the moment. Well, without having that rite I've already mentioned a few times (which violates the "convenience" property).
It's an open standard that everyone are building siloed systems on. It's exactly as you have said - I'm not locked in to any single company, but if I have devices or programs from multiple companies that bundle different implementations and don't let others in, I don't have any means to make them interoperate.
This could change someday. Fortunately, there is no fundamental design issue that prevents it. But I'm talking about what exists today and how the standard is bad for not even trying to address it, despite this being a very obvious issue.
I don't think that's the case. Yes, you'll have to wait a little while, but it's not like many sites support this today anyway. Very soon, most password managers will support it (KeePass does today, AFAIK), and then you can use your password manager as your Passkeys provider on all your devices.
And even if they will, they're at mercy of e.g. Apple letting anyone to replace iCloud Keychain with a third-party password manager. Which is also not possible yet. Probably the same for Android, although I'm not sure what's the situation there today. (But whatever it is, I would say that "well, don't use Apple/Google devices" is not an option for many in the current duopoly.)
All this can be solved, but the issue that is is not - today. So, today, I'm voicing my discontent.
> and then you can use your password manager as your Passkeys provider on all your devices
In an ideal world - yes. Sadly, I can't do this today with passwords, even though the world had spend many decades on trying to make things as seamless as possible. Over last year I've had to manually open a password manager on one device and type a password on another more than a few times.
The most obvious example is logging in to a streaming service on a smart TV - one step away from the normal conditions (scan-QR-code-on-my-phone flow not working) and typing password is the only option. Netflix is gonna love passkeys so users will possibly have slightly harder time logging in on others' devices ;-) BTW, sharing passkeys is also not exactly a solved issue - yet (even though some vendors made some promises).
Then, there's a case of accessing from untrusted devices (say, a net cafe). Theoretically, Passkeys should be a drastically superior solution to passwords - I would be able to plug in a security key, and it won't leak the keys, so even if a machine has a keylogger or network sniffer I'm still fine. In practice, however, enrolling a physical security key (Yubikey, Nitrokey, Solo) requires having it physically available, so it's always going to be inconvenient - and this is not changing until the standard extends or changes. Worse for multiple keys (I have four so every Webauthn sign-up is a pain in the ass). Because I'm most certainly not installing my password^W passkey manager on some untrusted machine.
