Per TurboTax:
"Now we'll help you upload your 1099-B since the IRS requires a copy
The IRS requires a copy of your 1099-B because you need to provide documentation for some of the transactions on your sales summary.
If you have a PDF copy, upload it and we'll send it to the IRS for you.
If you don't have a PDF copy, you can skip upload and we'll help you mail a paper copy."
