This was going to be my reply to Gary @ Emclient but they locked the thread before I could get back to him about the password request windows showing over and over again.
TO GARY (AND ANYONE ELSE HAVING ISSUES):
Be that as it may, maybe you guys should create a new document and explain that even the 2FA App Passwords will no longer work with emClient. I think many folks (including myself) we’re already aware of the “traditional” username and passwords no longer working with most modern applications. Most folks have 2FA and since emClient didn’t have an OAuth2 Option (at the time) then we had to generate an “APP Password” for clients that were not 2FA compliant. Evidently, that option is no longer available as well… HERE’s THE FIX: Remove the account, set it back up again (Using the OAuth2 Option (it’s automatic - nice!, now available in emClient) and you should be good to go. 
Seems like a miscommunications issue more than anything else at this point
Edited to correct grammar