Warning: SPOILERS for Superman & Lois season 1, episode 12, "Through The Valley of Death."
Superman (Tyler Hoechlin) did not turn evil in the Eradicator. Edge and his father, Zeta-Roh (A.C. Peterson), intended to have Kal-El's mind replaced with General Zod's so the Kryptonians could wipe out humanity and bring forth a new Krypton on Earth.
It seemed as if Superman & Lois was headed toward another iteration of an Zack Snyder's Justice League's future epilogue. In the Arrowverse Elseworlds crossover, there was also an Evil Superman created by the Book of Destiny. Superman & Lois also showed how the Evil Superman of John Henry Irons' (Wole Parks) alternate Earth conquered the world.
In Superman & Lois episode 12, Clark was indeed on the verge of losing himself to the Eradicator's mind-switching and Zod's personality even succeeded in briefly possessing Superman's body. However, John Henry Irons, who fully intended to kill Superman, instead did as Lois Lane (Elizabeth Tulloch) asked and urged Superman to fight the Eradicator. By focusing on Lois and his sons, Jordan (Alex Garfin) and Jonathan (Jordan Elsass), and the happiest moments of their lives, Superman heroically fought off Zod and permanently regained his true self. Although it was an internalized struggle, watching Superman reaffirm his personality was emotionally powerful. It showed that the Man of Steel is more than just the sum of his powers and that his heart and love are the true reasons why he's Superman.
Superman's humanity and capacity for good are often overlooked to enable him to become corrupted in Evil Superman stories. In Injustice and in Zack Snyder's dark vision, all it took was for Lois to die for Superman to crack like an egg and instantly turn evil, and this fundamentally misunderstands who Superman is. Superman III had the right idea because Clark was always within the twisted Superman fighting for his better nature, until they split into two and battled for dominance, with Kent emerging as the true Superman.
In Superman & Lois, Lois argued that Superman's love of humanity would prevent him from turning evil; ultimately she was proven right, although he needed help in the form of John Irons urging him to overcome Zod and the Eradicator. But the Arrowverse's Superman is very different than other versions because he's a husband and father who adores and is devoted to his family. This is an advantage other Supermen lack, which makes it easier for creators to justify Clark turning evil. Even the Evil Superman of John Henry Irons' Earth didn't have the family that Earth Prime's Kent has, and again, that was the real difference-maker.
In many ways, Superman & Lois is emerging as the most satisfying version of the Man of Steel since Richard Donner's Superman: The Movie in 1978. Clark has rarely been more relatable and more human than in Superman & Lois, while he's still properly awesome as Superman when it's time for heroics. So far, Superman & Lois has arguably been the finest exploration of Superman's humanity and the best balance of who Clark Kent is since he and Superman aren't alter egos but one and the same. By taking advantage of Superman & Lois' core premise of Superman as a loving husband and father, the series nobly rejecting the idea that the Arrowverse's Man of Steel could become an Evil Superman was pitch-perfect and inspiring.