Go to https://www.irs.gov/individuals/get-transcript, scroll down a bit and use the "Get Transcript Online."
Once you provide the identifying information, you can see the recent years' tax filings on record at the IRS. If it shows your 2019 return was filed, then it was sent in whether by TurboTax or you by mail. You can print a copy of the transcript for your record if you need it. Regardless, they have it on file.
If there's no record (might have a 'star' next to the filing year), then the system will respond with a form letter saying you didn't file a return for that year.
That's what happened to me when I checked because the IRS rejected our 2020 return. When I checked the transcript - no record of a return filed for 2019 - even though I have the TurboTax Electronic Postmark documentation and an email from Intuit/TurboTax saying the IRS had accepted my 2019 return last year.
The only solution I have to offer is what I did as trying to call the IRS help lines is absolutely ridiculous - it's like an electronic lottery to try and get in. And my guess is that they'll tell you to do something similar - and that's to mail in both your 2019 and 2020 tax year returns with the appropriate documentation from TurboTax about your filing information with a cover letter to explain why both returns are being mailed in. Also, when you print your returns, I'd suggest signing and dating both returns manually just to avoid any issues.
Even if they come back to say you filed your 2019 return late (simply because their systems can't handle the exception), you'll have all the documentation on file to point them to as well as your own copies (be sure to make a copy of the signature pages of both the 2019 and 2020 returns for your records).
Just my opinion and what we did to try to get this resolved - but adding to the 25+ million unprocessed returns pile that the IRS have/had when we sent them in.
