"I am stuck on where to reflect payments made in 2021, and after filing the 2020 tax return"

The extension due date is in October, and you intend to amend 2020, anyway.

"Include on 2020 Form 8915-E any repayments you make before filing your 2020 return. Any repayments you make will reduce the amount of qualified 2020 disaster distributions reported on your return for 2020. Do not include on your 2020 Form 8915-E any repayments you make later than the due date (including extensions) for filing your 2020 return. If you make a repayment in 2021 after you file your 2020 return, the repayment will reduce the amount of your qualified 2020 disaster distributions included in income on your 2021 return if you have spread the income over 3 years, unless you are eligible to amend your 2020 return."

"Amending Form 8915-EFile Form 1040-X, Amended U.S. Individual Income Tax Return, to amend a return you have already filed. Generally, Form 1040-X must be filed within 3 years after the date the original return was filed, or within 2 years after the date the tax was paid, whichever is later.

Qualified 2020 disaster distributions. If, after filing your 2020 return, you make a repayment, the repayment may reduce the amount of your qualified 2020 disaster distributions reported on that return. Depending on when a repayment is made, you may need to file an amended tax return to refigure your taxable income.If you make a repayment by the due date of your 2020 return (including extensions), include the repayment on your amended 2020 Form 8915-E."