I hear your frustration and agree that it's bizarre that this software company can't prefill the What-If worksheet very accurately. It's unbelievable. It's been there for at least a few years because I used it first for my 2020 return, I think.
I just wanted to chime in again to say that it's given me a workable estimate of taxes we each owe if I go through it and correct it. You can edit it and move the numbers in each row to the correct columns, and it recalculates.
