i'm not sure what you are doing but a rule for the 1256 carryback is that you can not create or increase an NOL as a a result of a 1256 c/b to that year. I don't know if Turbotax will generate a computation of an AMT NOL but I wonder why you would have one for 2019,
do note that when you do 2019 amended the AMT c/o form 8801 form will change and that will need to be reflected when doing 2020. The NIIT tax is a year by year tax and so each year's should stand on its own but will probably be reduced due to lower income for each year.
