I mentioned Bitwarden in my comment, and my frustration specifically comes from occasions that I had Account X ready in Bitwarden, started up an app that relied on Account X, but loaded an HTML login page that had no discernable controls to use that Bitwarden passkey; expecting entirely for it to exist in my Apple keychain, which I never use.

I think it's very easy to claim this specific app / account was not implementing passkeys well. But if that's the case, how can I guarantee any other accounts I move over won't fuck it up somewhere? I haven't seen anyone get the concept of passwords wrong, and even if they don't understand how managers work, I have control of the copy-paste function and can even type a password myself if needed.