Superman Returns left the story of Brandon Routh's incarnation of Clark Kent open-ended but 13 years later, Bryan Singer's 2006 movie was canonically made a part of The CW's Arrowverse in 2019/2020's Crisis On Infinite Earths crossover. Although Superman Returns was intended to relaunch a new movie franchise for the Kryptonian hero, its disappointing box office prevented a sequel from being made. Routh's comeback to the role in Crisis gave his version of the Man of Steel (and his fans) a fitting conclusion while filling in some details as to what happened to his Clark Kent after Superman Returns ended.
A sequel vaguely set five years after Superman: The Movie and Superman II, Superman Returns continued the story of the Man of Steel while ignoring the events of Superman III and Superman IV: The Quest for Peace. Routh stepped into the role originated by Christopher Reeve and was playing the same character, who returned to Earth after traveling to the remains of Krypton. Once back home, Clark resumed his career as a reporter for the Daily Planet, only to find that his love Lois Lane (Kate Bosworth) had moved on, was engaged to Richard White (James Marsden), and had a young son named Jason (Tristan Lake Leabu) - but Superman was really his father. More alienated than ever, Superman also has to contend with his arch-nemesis Lex Luthor (Kevin Spacey), who used Kryptonian technology to create a Krypton continent. But Superman prevailed over Luthor and found his place once more as Earth's protector while also looking out for his young son.
Superman Returns' universe laid dormant for 13 years before Routh agreed to reprise the role in Crisis On Infinite Earths, and his film was retroactively made part of the Arrowverse along with the Reeves movies. In an unexpected bonus revelation, The CW answered what had happened to this iteration of Superman in a way that planned sequel Superman: The Man Of Steel was never able to.
In the canon of The CW's Multiverse, Superman Returns' world was designated Earth-96 and Routh's Superman played a key role in the Crisis. In fact, the movie Superman was designated as the Paragon of Truth, one of the seven most important superheroes in the Multiverse. Further, Routh's Man of Steel not only carried the legacy of his film and Christopher Reeve's films but he also blended elements of the Kingdom Come Superman from DC Comics, as symbolized by his 'S' crest with the black background.
While Crisis On Infinite Earths only filled in portions of what Clark Kent's life had become since Superman Returns ended, the details were fascinating. Clark did marry Lois and he became Editor-in-Chief of the Daily Planet, but his promotion was borne out of tragedy. "A reject from Gotham" (implied to be the Joker) took issue with the coverage he received in the newspaper and he gassed the Daily Planet building. The criminal's "practical joke" tragically left behind numerous casualties, including Lois Lane. But thankfully, Jason was safe from the attack. As Kingdom Come Superman, Clark changed the colors of his S symbol to remind himself that hope still shines through in the darkness.
In the Crisis, the Lex Luthor of Earth-38 (Jon Cryer) used the Book of Destiny to briefly mind control Routh's Superman, who then fought his counterpart Superman from Earth-38 (Tyler Hoechlin). But Earth-96's Man of Steel soon returned to his heroic self and he did his part to help stop the Multiverse from collapsing - until Luthor again used the Book of Destiny to kill him and assume his place as the Paragon of Truth. However, when the Arrowverse's heroes defeated the Anti-Monitor (LaMonica Garrett) and rebirthed the Multiverse, Earth-96 was restored. Routh's Superman restored his classic yellow and red S shield and he took his place as his world's greatest hero, delivering on his Superman Returns promise that "I'm always around."
Crisis On Infinite Earths also indicated that elements of Superman III and IV were also retroactively restored. Routh's Clark admitted, "I once went nuts and fought myself," referencing Kent facing the evil Superman in Superman III. The Kryptonian also copped to "several go-arounds" with Lex Luthor, which may have involved the events of Superman IV. In any case, with no Superman Returns sequels in the cards, Crisis On Infinite Earths can be considered by fans as the canonical ending to (and new beginning for) Brandon Routh's Superman.