Sorry, but without knowing what the purchase agreement provided, I don't think anyone can say for sure what occurred was reported properly. Further, there was no stock sale, you had an interest in a partnership (form 1065) so what occurred was either a purchase of the partnership assets (most likely since you continued to receive a k-1 in the ensuing years) or purchase of the partners' interests.
with a sale of the partnership assets, the entire reporting should have been done through the k-1. the partnership would receive all the money and would distribute some or all to the partners. this seems consistent with what was reported in 2018.
in 2019 all that was required of you was to report on your 1040 the k-1 activity based on what was on the various lines in PART III
in 2020 apparently the only thing that occurred was the partnership received the balance of the cash for the sale of its assets and made a distribution to you of your share of the cash. assuming that schedule L on the k-1 was always on the tax basis, then there is nothing to report on Schedule D in 2020
any entries you made in the Turbotax k-1 schedule L go nowhere. there not used by Turbotax or for that matter any other tax software of which I'm aware.