currently importing a CSV for stock trades is not possible. even importing CSV for digital assets is on hold.
if your broker partner's with Turbotax a direct import of the 1099-B is possible (at least for some. There have been numerous threads reporting import failure)
there is an alternative
You can enter summary totals for each category on the 8949 with code M. then you need a copy of that CSV printed out or a copy of the 1099-B sent from the broker. You mail it with Form 8453 following the form's instructions
https://www.irs.gov/pub/irs-pdf/f8453.pdf
