After fiddling with various ways of entering the Est Tax payment amount on TurboTax's "internal" Tax Payments Worksheet, I found the following workaround to be fairly straightforward and easy to implement:
In order to have the correct amount appear in column (a) of line 19 of Form 2210, the list of Fed Est Tax payments entered/recorded for TurboTax's "internal" Tax Payment Worksheet is deliberately "tweaked" in a certain way, carefully maintaining the correct Total of such payments. Specifically, what would have been the second entry in the list of payments on that Worksheet gets recorded as a pair of payments, in the following amounts: $0 and the true amount of the payment. This pair of payments then become the second and third
entries in the list of Fed Est Tax payments on that Worksheet. (The essential "trick" seems to be make the second entry in the list of Fed payments on the worksheet be a zero-value "throwaway" entry, because it will be ignored by the calculation error. It's sort of analogous to how the second column of Section A of Form 2210 is not used, or ignored, due to combining the first 2 quarters of 2020 into the first column of that form.)
For example, in my case, an actual Fed Est Tax payment made on 6/15/20 in the amount of $2,300 is recorded as a payment of $0 (as the second entry in the list) and another payment of $2,300 (as the third entry in the list) , both on the same date.
