Update after talking to live support:
So, after sharing my screen with the phone support agent and her investigating, I was told that it's not possible to e-file an amended return with the desktop version of TurboTax, only the on-line version. It has to be e-filed. Initially, I suspected the problem was that I failed to save a separate copy of my unamended 2022 return. The app doesn't prompt you to do that; you just have to know by reading some other instructions. Based on the screens I was seeing, it seemed that the TurboTax app was thinking that I was trying to file a regular 2022 return again. In any case, printing, mailing and waiting a long time are in my future.
If that is, truly, the right answer, TurboTax could have saved me some time and effort by not leading me down the e-file path. A tactically placed info screen might be appropriate.
UPDATE: I gave up and mailed it in. That in itself was confusing, as there is differing and slightly ambiguous information on-line ( including the 1040ZX instructions) as to what forms to be included. I guess I'll find out in another six months if I did it right.
