SirBlain,
If you're using Windows Hello Face, Fingerprint or PIN, you're already using FIDO 2 standard Passkeys, since that's how Microsoft gets you logged into Windows with the passkey system before you could normally use them from within the web browser.
The reason that Microsoft is forcing the use of passkeys is simple, the password is totally and utterly dead as a security feature, since it's too easy for bad actors to acquire these either via website breaches, phishing or simply getting the general public to hand them over, especially those over 50 as you mentioned, since they're generally befuddled by any authentication method regardless of how supposedly 'simple' some think it might be.
The true major problem that Microsoft has right now is the rampant loss of Microsoft Personal accounts by those of all ages, especially those using games which are a high-value target. Stopping this or even slowing it will require multiple factor authentication and the older methods of phone Text and even email are aging quickly, since they're just as prone to phishing and other more technical attack methods as email.
Passkeys, on the other hand, were designed to be phishing proof and use modern encryption techniques, while they technically require relatively little of the user himself to either set up or especially to use once they're in place.
However, you are correct that with Windows 10, the passkey support is minimal and thus relatively difficult, while even with Windows 11, the interfaces are too varied and inconsistent, simply adding to the confusion for a system that as you already noted, is completely new and unfamiliar to anyone, let alone older users.
Apple, Google, Microsoft and many others worked hard on the technology to make a highly complex system work fairly well, but it's the less technical user interface where they didn't take the time to focus their efforts on making that both simple and consistent and test with real everyday users rather than the techno-geeks who can figure it out and eventually make it work themselves.
So, you're right about the support issues, at least until they realize the true problem isn't the technology, as always it's the people, so they'll either need to properly support Windows 10 or simply drop that completely, along with working with the other major FIDO 2 members to make their interfaces at least relatively consistent across platforms and with website owners to make theirs consistent for adding and using the passkeys as well.
Even with my 50-year history using, managing and supporting computers and security, I found the Windows 10 passkey interface difficult at best and decided to stop trying to use it until I purchase a Windows 11 system next year. Since I haven't got this presently, I'm not sure how well passkeys work with Windows 11, so I can't say what precise issues remain and which are due instead to problem hardware or manufacturer implementations of Windows Hello for example, so I can't truly comment on those.
I do know there are problems though, so just like the Microsoft Authenticator app I use with ease every day, I know that some will have more problems than others using these more secure but technical tools, which unfortunately Microsoft and the other major platform developers can't afford to wait to implement until our Baby boomer generation kicks the bucket.
Rob