Warning: SPOILERS for Superman & Lois Season 1, Episode 13, "Fail Safe".
Superman & Lois episode 13 gave John Henry Irons (Wole Parks) a role traditionally held by Batman: Steel was handpicked by Superman (Tyler Hoechlin) to be the one to kill him with Kryptonite weapons if he ever turns evil. In last week's Superman & Lois, Irons was instrumental in helping the Man of Steel fight off being possessed by General Zod. With John's help, Superman overcame the Eradicator's power and regained his true self but the Kryptonian hero also knows something similar could happen in the future and the world needs to be prepared.
The idea that Superman chooses a trusted friend to terminate him if he becomes evil came from DC Comics. The 1990 story Dark Knight Over Metropolis saw Superman and Batman team up to acquire a Kryptonite ring formerly owned by Lex Luthor. Superman's arch enemy created the ring as a defense against the Man of Steel but it ended up giving him cancer and was later stolen. At the end of the story, Superman makes the pivotal choice to give the Kryptonite ring to Batman care with the instructions that the Caped Crusader is to use it to end Superman's life if the Kryptonian ever turns on humanity. The concept of Batman having Superman's blessing to kill him with Kryptonite was adapted into other media like the Justice League animated series. Of course, Batman V Superman: Dawn of Justice tweaked why Batman (Ben Affleck) acquired Kryptonite for the express purpose of saving the world from Superman (Henry Cavill).
In Superman & Lois, Clark Kent learned about Project 7734, a Department of Defense initiative led by General Sam Lane (Dylan Walsh) to stockpile Kryptonite weapons to use against Superman if he turns evil. This arsenal includes a prison cell to hold Superman, plus "two dozen rifles and handguns, a few thousand Kryptonite bullets... a substantial collection of knives, swords, spears... and five or so biochemical weapons in various stages of development." These were made from "a couple of warehouses worth" of raw Kryptonite. Rather than be alarmed at this stockpile of lethal weapons intended to kill him, Superman agreed this fail-safe was necessary. He later chose John Henry Irons to be the one to use 7734 against him since he trusts the alien from another Earth and Irons originally came to Earth-Prime to kill the Man of Steel.
It makes sense that Superman & Lois slotted John Henry Irons into the role of Superman's potential executioner since there is no Batman in the Arrowverse. Batwoman confirmed that Bruce Wayne has been missing for years and, although Supergirl established that Superman and Batman are friends, that was pre-Crisis On Infinite Earths and there has been no mention of Batman in Superman & Lois. Then again, since Batman is MIA, it's also logical that Clark would turn to John Henry Irons to take what's traditionally been Batman's job. John proved himself to the entire Kent family and is trusted with Superman's secret identity, but he's willing to do what's necessary to protect the world from an Evil Superman.
What isn't clear is how Project 7734 would affect Supergirl (Melissa Benoist). The Girl of Steel has also been briefly turned evil in the past and has faced evil doppelgangers like Red Daughter. While much of that happened pre-Crisis, the guest appearance of John Diggle (David Ramsey) in Superman & Lois reaffirmed that the show is still very much part of the Arrowverse. Yet Clark's cousin Kara Danvers isn't referenced on the show, despite the fact that she would certainly have opinions about an arsenal of Kryptonite weapons that could be used on her as well as Superman - and the fact that Project 7734 has Clark's blessing.
Superman & Lois episode 13 also featured a compelling debate between Clark and Lois Lane (Elizabeth Tulloch) about the necessity of Project 7734 as a fail-safe to protect Earth and why Superman is afraid he could be corrupted again. In DC Comics, Superman would automatically turn to Batman as the person he would trust to put him down if he becomes Evil Superman. In Superman & Lois, John Henry Irons is the best substitute available for Batman.