I just had this problem working on my 2020 return and TurboTax
told me my 2019 file was too big. I went back to 2019 and went to "print returns" and then looked at the 2019 PDF that was 80 pages long. I figured out that I only wanted to import the 2019 federal detail and then made a new PDF retitled "myname2019FedOnly" that was only pages 7 to 42 of my 2020 entire PDF. I then was able to import it successfully to my 2020 file
