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/
Start the 2024 online tax return by entering some personal information then click on Tax Home on the left side of the screen.
On the Tax Home webpage -
Scroll down to the section Your tax returns & documents. Click on the Year 2021 and Click on Download/print return (PDF)
If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.
IRS says they did not receive the return at all? Or did they say you owed tax due and did not pay?
Check your TT account to see what it says for 2021. Does it show that an e-file was accepted? Or does it say something else like "rejected", "printed," or "ready to mail?" If it does not say accepted, then you need to print it now, sign and date it and mail it in.
Or, if it says accepted, your only proof that you paid your tax due is your own bank or credit card records. Do you have proof? Did you forget to pay?