Today I was scratching my head as to why I couldn't set my newly installed Windows 10 Pro system to automatically login (which is a requirement for some of the software that I'm running as this will be a home server). Due to the fact this is a new clean system, I decided to set it up with the latest version of Windows 10 at the time (20H2), instead of just using the previous USB stick I had created. I then installed using my Microsoft account as the main administrator user and setup a login pin, instead of a local account (which is the important point here).
Now going back to the original title of the post, if you're not sure how to setup Windows 10 to automatically login, there are endless tutorials online (here is a example from TechJunkie). Unfortunately all of these tutorials run into the same issue, they assume that the 'Users must enter a username and password to use this computer.' option is visible. However, if you install and setup Windows the way I had above, the option won't be visible, and therefore you won't be able to select it.
After much confusion and cross checking my other systems, I finally worked out what the issue was. By default the option 'Require Windows Hello sign-in for Microsoft accounts' was enabled when I installed the OS (this can be found under Settings > Accounts > Sign-in options), which normally wouldn't be an issue... But because I'm trying to get the system to login automatically by providing my password this won't work. This is due to the fact that Microsoft's remote online login system will now be enabled and your password will never be entered into the local system. Noting that that I also use 2 factor authentication and the authenticator app which meant that I didn't actually login with my password to begin with.
So to make a long story short, just disable the 'Require Windows Hello sign-in for Microsoft accounts' option and the 'Users must enter a username and password to use this computer.' checkbox will magically reappear.
