Does the IRS say you did not file a 2020 return---or do they say you did not pay your 2020 tax due? If you owed tax due for 2020, your only proof that you paid will be your own bank or credit card records. What does it say in your TurboTax account for 2020? Does it show that your return was "accepted,", "rejected,". "printed," or "ready to mail?" If it says anything other than accepted, then you did not file it unless you put it in an envelope yourself and took it to a mailbox. If the return was truly not filed, then you can still file it. It cannot be e-filed; a 2020 return can only be filed by mail. You will need to print it, sign and date it in ink, and mail it in.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.
Refunds for tax years 2020 or earlier have been forfeited and will not be paid to you even if shown on the tax return form. But if you owe tax due, you will still have to pay, and you will be billed later for the interest and penalties owed. TurboTax will not calculate the penalties or interest. That will be done by the IRS/state after they receive your return with your payment of the tax due as shown on the tax form(s).