How does Turbo Tax think you didn't file? Why does it matter? Did you use the Online browser version or the Desktop installed program?
Did you efile? Was it Accepted? Did you go all the way through the File tab, through the 3 steps and hit the big orange Transmit Returns Now button? Maybe you didn’t finish filing it or it rejected.
Check back though your emails. When you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepted or Rejected your efile. If you efiled there should be an Electronic Postmark page. Probably near the end. That is your proof and signature
When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. What does it say?
How to Access prior year online returns
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/270...