This answer was enormously helpful. To clarify one point, though, TurboTax 2020 Premier desktop version has been changed to address this issue. A notation is, in fact, put on the dotted line of Sch A, line 11. HOWEVER, the number it puts there is not correct, and there are some really screwy things going on with the math as it relates to 100% cash donations. I set up a dummy return to see how the current version works. I entered a fantasy donation of $1,500,000 and the software increased it to $1,935,342 for some reason. There are two forms and a handful of worksheets that address charitable donations up to 100% of AGI and they are not producing accurate and consistent results. This needs to be fixed before we all start filing in 2021.
