@wmpyoungx
Thank you. I, as well, checked Box D (in Part II). I also did an "alternative" return this morning and did not do a Form 2210. My penalty in both is identical (and negligible.)
So, I think I'll go with the "alternative" return and not filing a Form 2210, just take the penalty.
Of course, I'm not in any hurry to file. I usually wait until the first week of April in case my brokerage wants to amend (change) any 1099-Div or 1099-B. So, maybe over the next 5+ weeks we'll see clarity on Form 2210. However, based on your thoughtful "deep dive" we may already have it.
By the way, my entry for line 11, column (a) reflects (to the penny) my total of withholding and estimated payment. My overpayment from 2020 (which I applied to my 2021 return) is not reflected.
I download (PDF) the return with all calculations. When I take a look at the "Underpayment Penalty Worksheet" my 2020 overpayment is not credited until installments 2 & 3 (6/15/2021 & 9/15/2021) respectively. Oh yea, the Underpayment Penalty Worksheet is NOT filed, it's for our personal records.
