Enable FIDO2 security key login on onedrive.live.com
If you try to login on onedrive.live.com: https://onedrive.live.com/about/en-us/signin/ - the option 'Sign in with a security key' is missing. It appears to be a cut down version of the usual Microsoft sign in form: https://login.live.com/login.srf , which is weird.
The security key logon option appears on login.live.com, along with 'sign in options'. It also appears if you login through outlook.com > sign in.
This is a problem because it makes logging directly into OneDrive inconvenient. You have to login through the second link, then navigate to OneDrive again.
This seems like a bug. The sign in page should be uniform no matter which Microsoft service you try to log in to.