You can't do it.  TT can convert to PS, but not the other way around.

@Just-Lisa-Now- 

You misread my question.  I am trying to transfer/import a 2020 TurboTax file into ProSeries.  The file is a desktop file that was downloaded from TurboTax Online.

That's correct.  For some reason ProSeries can't import/transfer the downloaded file from TT Online.

Boo Hiss proseries.  Why this doesn't work is frustrating for tax professionals.  Get your act together and resolve this.  I have new clients that used TTO and they now need professional help and I have to redo their entire return because you wont let us import the file.

It's not frustrating for me - I have never done that.  Besides, look at the bright side - you can charge them more now that you have all that work to do.

Intuit provides directions for how to get a TT online datafile to the desktop, then converted by using TurboTax Desktop program. That should make the file that is then used for ProSeries. They also cover what to do if you have errors, and that the Tax Year matters.

If you can’t get it to work, Call tech support. Proseries has a conversion team that might be able to accommodate it.