Thanks to @VolvoGirl and @SteamTrain for your constructive skepticism. I followed your clues to find that I entered estimated taxes in two places – the correct ...
I found the Tax Payments Worksheet, and it looks like TurboTax double-counted my estimated tax payments. These payments appear in the "Tax Payments Other Than W...
I use TT Online, and despite the IRS saying e-filing is available for 1040-X, for tax year 2019, TT has still not enabled this. My accountant has warned me not ...