As for Nebula, I’m not sure she needed the revenge by the final battle of Avengers: Endgame. Her trauma was exposed in Guardians of the Galaxy Vol. 2, which allowed she and Gamora to become real friends and sisters. As for Thanos, she did get a final confrontation with him in the opening sequence of Endgame. The Mad Titan admits he was too harsh on her, right before Thor unceremoniously decapitates the villain. From there, Nebula is given five years to grow as a person, and connect with the remaining survivors of Thanos’ snap.
Article source: https://www.cinemablend.com/news/2495480/avengers-endgame-writers-explains-why-nebula-didnt-wear-the-infinity-gauntlet