Good job Lisa!

I just went down that rabbit hole and tried to follow the flow on all of the forms.  You end up in a worksheet on the 1040 instructions to Schedule 3.  Line 10 says:

"You can defer payment on up to the amount on line 10 until 12/31/2021
or 12/31/2022 by reporting the amount on line 10 above (or a smaller amount)
on line 12e of Schedule 3 (Form 1040)"

and then Line 11 of that worksheet:

"Enter the amount you reported on Schedule 3, line 12e"

Are we having fun yet!?!

Edit: https://www.irs.gov/pub/irs-pdf/i1040gi.pdf

See PDF page 102.