Update: I resolved the rejection by re-entering Turbotax 2020 and changing my spouse's 2019 AGI to zero, while keeping my 2019 AGI at the 2019 1040 Line 8B amount, which I knew was correct. The IRS accepted it. But I still don't understand why the Turbotax 2020 interview demands separate AGI amounts for a 2019 return that was filed jointly. There is no such thing. I think there is a fault in the Turbotax 2020 software because I didn't have this problem last year and the scenario was exactly the same.
