User mims77 posted a solution to the issue with the unintentional values appearing in Line C -- "N/A" in my case.
The issue is that the 8915-F was populated by a literal "N/A" in a field that was expected to be blank or to have a specific code in Line C of the form.
In Line D, a checkbox indicates that it's not one of the declared disaster codes, but is instead Covid-related (mine was). This means that line C must be blanks and only line D is to be checked.
So, the solution is:
Write down the values that are in the 8915-F. It's typically 1/3d of the amount that was withdrawn due to Covid in some of the lines. Which ones are specific to your tax situation.
Go to Tax Tools in the lefthand menu.
Click Delete a Form.
Find and delete the "2020 Qualified Distribution" worksheet. You cannot (and need not) delete the 8915-F form. It will be automatically removed when you delete the 2020 Qualified Distribution worksheet.
Go back to Income, and revisit the 1099-R section.
When the questions come up about your 2020 distribution, click the checkbox indicating it's for Covid then fill in the values that appear beneath. The numbers you copied from the previous (erroneous) form.
Click through until you reach the E-File section. Just before you file, you'll be presented with a button to view or print your prepared forms. You can view, make a copy, print, etc. But from here, you can visually confirm that form 8915-F has nulls across all fields in Line C and that only the checkbox in Line D is checked.
