I can't find my in progress 2020 return.

A 2020 tax return can only be printed and mailed, it cannot be e-filed.

You will have to start a 2021 tax return using the exact same User ID that you used to create the prior year online tax return.  Once some personal information has been added to the 2021 tax return the section for access prior year returns will be visible.

To access your prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Scroll down to the section Your tax returns & documents.  Click on the Year and Click on Download/print return (PDF)

Print, sign, date and mail the tax return to the IRS.  Include with the mailed return any forms W-2 and 1099 which have taxes withheld.  Go to this IRS website for mailing addresses - https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment

There are no penalties for filing a tax return after the due date if filing for a tax refund or there are no taxes owed.