My system admin showed me the screen he had where it has the option to reset my account password. On the same account settings page there was another option to clear all Sign-in/Device history. But I don't recall exactly what the test of the option says (and don't have admin access myself to view the same page). But it essentially forced my account to be signed out of all trusted devices. After that was done, I was then able to try signing into the Authenticator app using just my email and password and instead of it asking me to approve the sign in (on the authenticator app I was trying to sign into) it instead asked me to provide a secondary contact option as either an alternate email, or a phone number. I was able to input my cell number and then get a SMS code sent to my phone to authenticate it and then sign into the Authenticator app by again getting a SMS code to approve the sign in.
So somewhere in the Microsoft system, it thinks your account is already signed into the authenticator app on some device. So you have to tell it to sign you out of any and all devices, which then resets the options for secondary authentication.