An extension request for a tax year 2020 tax return had to be submitted on or before 05/17/2021.
There are no penalties for filing a 2020 tax return after the due date if no taxes are owed or there is a tax refund.
Tax owed were due and payable on or before 05/17/2021 to avoid a failure to pay penalty and a failure to file penalty. So if you have taxes owed the tax return needs to be filed as soon as possible.
Federal taxes owed can be paid on the IRS payment website using Direct Pay - https://www.irs.gov/payments/direct-pay