Cannot set up sbcglobal.net email account

AT&T recently upgraded security on their email. It now requires OAuth. According to their web site, Apple devices support this capability. On an iPhone XS, running the latest iOS, I am taken through an endless loop of change password screens. I even tried using a Security Key generated from the AT&T Profile, (which resolved the issue with Thunderbird), but even that does not work on the iPhone. local Apple stores and their Genius Bars are closed, as are nearby AT&T stores. Please help.