The main problem in the "Goku Black" arc of "Dragon Ball Super" revolves around the emergence of Goku Black, a mysterious antagonist who possesses Goku's body and wields immense power, alongside Zamasu, a Kai who seeks to eradicate all mortals. Goku Black's existence poses a significant threat to the safety of Universe 7 and leads to the destruction of Future Trunks' timeline.
The primary conflict stems from Zamasu's ideology that mortals are flawed and should be eliminated to achieve a "perfect" universe. This culminates in Goku Black and Zamasu's plan to create the "Zero Mortals Plan," which involves using the Super Dragon Balls to gain immortality and eradicate all mortals.
The resolution of the arc occurs when Goku, Vegeta, and Future Trunks work together to confront and battle Goku Black and Zamasu. After several intense battles, they struggle to overcome their foes. The turning point comes when they realize that Zamasu's immortality makes him nearly invincible. Using the Potara earrings, they fuse into Fused Zamasu, who becomes even more powerful. However, Goku and Vegeta find a way to defeat him by using the Spirit Sword technique and utilizing the power of Future Trunks' Spirit Bomb, ultimately leading to the destruction of Fused Zamasu.
The arc concludes with the remaining characters using the Super Dragon Balls to wish for the revival of the people who were killed by Zamasu and restoring peace to the timeline. This resolution emphasizes themes of unity, friendship, and the struggle against tyranny.