That second link from philc43 is the fix. I had come across it in my previous searches, BUT I missed that OPTION FOUR of the link is the fix.

For anyone who doesn't have an active admin account. ...

Thank you Night Hawk. The link you posted to Brink worked:
Administrator account - Enable or Disable in Windows 10 - Windows 10 Forums

The option I needed was OPTION FOUR.

I used the disc...

I too have this issue. Windows 10 allowed my only active user, which was also an admin, to remove itself from the administrator group. I don't think past versions of Windows allowed this to occur. ...

Basically, when I setup my system I run my primary user as an admin to install and set everything the way I like it. After a week or so I remove my primary user from the Administrators group. I...