I have good news to share to the members of the community struggling with this issue. I have just filed all my returns and am waiting for my refunds. Now, here is the issue, and the fix.
I had RSUs which I sold in 2020. My custodian, Fidelity, issued to me a 1099-B with all the crucial information, and ONLY SOME OF IT DOWNLOADED TO MY TURBOTAX RETURN. Revealingly, all the transactions were losses but: (1) Fidelity knew, and reported to me on the 1099-B, my basis on all the sales, but did not report it to the IRS (Why?) Instead, it reported the sales as gross to the IRS, and withheld substantial amounts that were not due, because the trades were losses, (2) The download to Turbotax did not include the basis for each of the sales, which I had to enter manually.
The problem in Turbotax was that it kept throwing errors on my Federal return relating to the 1099-B. In every case where I entered the basis, Turbotax followed it with another screen asking for information about the vesting of the RSUs. I had left that blank on all the entries. Who needs to ask about vesting? You can't sell shares you don't own!
The fix was that for each entry, I went to that additional screen and just entered the number of shares in each lot sold. That very same number already appeared in several prior fields. For some stupid reason, that number of shares did not auto-replicate from one screen to the next - for the same transaction -- and that caused the problem.
That is the fix, folks. When you get to the screen in the worksheet that is throwing errors, just make sure that you have the number of shares sold in the top line and close out of that entry and move on. It will then clear the error check and you can file.
Shame of Turbotax for a stupid software error. Shame on both Turbotax and Fidelity for not automatically downloading the basis data that Fidelity had.
