When a partner donates services in $2019$ to a partnership in exchange for a partnership interest that contains a substantial risk of forfeiture until $2021,$ the partner can:

Elect Section $83($b$)$ in order to be taxed in $2019$ on the value of this interest in $2019.$ If the partnership interest never materializes the partner could then deduct that same amount he picked up as an ordinary loss in $2021.$

Cannot be taxed in $2019$ under any circumstances.

Section $83($b$)$ will allow any taxed amount in $2019$ to be treated as a LTCG$.$

A Section $83($b$)$ election could result in the service partner picking up a smaller amount of ordinary income in $2019$ because the interest is difficult to value, with the potential to mostly cash out with a LTCG in $2021$ if success occurs.

None of the above.$$