when you import - GENERALLY, all the necessary info is transferred from the broker into a 1099-B worksheet in Turbotax - description, data acquired, date sold, number of shares, sales price, cost basis, wash sale amount ( If applicable) so there is USUALLY nothing for you to enter.
exceptions cost basis for fractional shares when the broker reports $0. Then, at least in 2020, the cost basis is left blank which Turbotax deems an error and will prevent e-filing until a cost - even $0 is entered
There could be other situations where the info is incomplete or incorrect - tax basis for securities transferred from another broker, tax basis for investments in master limited partnerships, or publicly traded partnerships
Turbotax does not guarantee the accuracy of the imported info just like it doesn't guarantee the accuracy of the data you enter manually. it is your responsibility to review all imported data for accuracy
