The instructions given here are missing a crucial step. After you "sign in, open, and continue your return" you have to take another step to download the 2020 file.
Once the online 2020 is opened, click on the "Finish and File" section of the return, and the click "Continue," even though you're not going to actually file your return.
Once you're on the "File your Return" screen, then go to the left menu, look for Tax Tools, and then Tools. You *should* now be able to download the work you've already done on your 2020 online return and open it with the desktop version.
