If the LLC dissolved and it was treated as a partnership for tax purposes, then yes, the partnership ended in 2018.
You will need to report several items. First, the items shown separately on the final Sch K-1.
Then in addition to that, you have a partnership interest (a capital asset) that was also disposed of. You need to calculate the basis in that interest after taking into account the final K-1 items.
If you received any money, property, relief of debt, etc., etc. when the partnership ended, that would be in exchange for your partnership interest. There normally would be some gain/loss on anything received and the basis in the partnership interest.
Here is a link to Publication 547, Partnerships. This should help give you some guidance
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://www.irs.gov/pub/irs-pdf/p541.pdf
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