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@Totallyi On 2020, I'd go back into your return, tell TT you're amending, and enter the K-1.  See if it changes your taxes.  If it does, you can refile.  If not, you won't need to.  But either way, entering the K-1 into the 2020 software will tell you what the carry-overs are, and you'll get to use those carry-overs when you sell.

As to the partial sale in 2020, I don't want to make assumptions about what the different boxes on the Sales Schedule are (sales schedules aren't all standardized), but to generalize:

• You'll need to enter the K-1 into TT.  It'll handle the entries you mention on box 11 and box 13.  Combined with the entries from 2020, TT will record the income and losses in the right places.
• On the USO Sales Schedule is there anything about Ordinary Income?  If not, you'd enter 0 for everything on the sales screen.  If so, you have to do the bit about entering the Ord Income on the sales screen, and also entering its inverse on the Partnership Basis.
• Either way, you then go back to the 1099-B and change the cost that's reported there.  The Sales Schedule should give you a "Adjustment to Basis" number.  You add it to what you paid.
• On the Describe the Partnership screen, you'd check the "PTP" box, and the "partial disposition" box.