Does the IRS say you did not FILE a 2020 tax return or do they say you did not pay your 2020 tax due? Your only proof that you paid would be your own bank or credit card records. TurboTax never knows how, when or even if you paid the IRS.
You have to access your own account and/or print it for yourself using exactly the same account and user ID that you used when you prepared the return.
Start a 2023 return online and enter some personal information so that the menu on the left opens up and lets you access your past year returns.
Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
https://ttlc.intuit.com/questions/1901535-forgot-your-turbotax-online-user-id-or-password
https://ttlc.intuit.com/questions/1901486-how-many-turbotax-accounts-do-i-have
Or did you use the desktop version of TurboTax? If so, the files are on your own hard drive or any backup device you used like a flash drive.
https://ttlc.intuit.com/questions/1901659-find-your-tax-data-file-in-mac
You can get a free transcript from the IRS or for a fee of $43, an actual copy of your tax return.
https://www.irs.gov/individuals/get-transcript
https://www.irs.gov/pub/irs-pdf/f4506.pdf
If IRS can't find your 2020 tax return, IRS says:
"submit another 2020 tax return."
May 18 is the last day to file for a 2020 tax year refund.