Superman & Lois not being set on Earth-Prime calls into question what Clark knows about "Crisis on Infinite Earths". The Man of Steel was a key player in the Arrowverse crossover event and even served as one of the Paragons chosen to fight the Anti-Monitor. However, it's since been revealed that this is not the version of Clark Kent Hoechlin plays in The CW's Superman & Lois show.
In the Superman & Lois season 2 finale, General Sam Lane commented on how Clark is the only superhero on the planet, essentially confirming the reason why characters like the Flash and Supergirl haven't been joining in the action. Apparently, Superman & Lois is set on a duplicate Earth in DC's multiverse. By heading in this direction, Superman & Lois has opened the door for new interpretations of existing Arrowverse characters, such as Lex Luthor, to join the series. It also changes the history of its take on Superman, who had experienced a few adventures in the Arrowverse prior to the beginning of his new show.
Superman & Lois Hinted At Clark Knowing About The Crisis (But How?)
One of the stories the series has removed from Superman's past is his role in the Crisis. Superman still helped save the multiverse, of course, but that was a different Clark. Since that's the case, it's worth wondering if Superman & Lois' version is even aware that the Crisis even happened in the first place. He wasn't involved in that fight, yet there has been a hint that both he and Lois have at least some knowledge of the event occurring. Back in season 1 when they still knew John Henry Irons as "Captain Luthor," Lois brought up "everything we know about the multiverse now" as they considered the possibility of him being a Lex Luthor doppelganger.
Obviously, the implication of this comment was that Clark and Lois recently met characters from another Earth. At the time, this reference made sense given the fact that the Crisis had only just happened during the timeframe of season 1. But now, this exchange is much more confusing. One possible explanation for it is that it's simply a plot hole. But, Superman & Lois showrunner Todd Helbing has maintained that the decision to keep the show out of the Arrowverse was made in season 1, meaning that its separation from Earth-Prime should have been known before this line was written.
Clark May Have Had Multiverse Adventures Before Superman & Lois
Whether Lois' "multiverse" line was a mistake or not, one way it can be interpreted going forward is that the show's version of Superman engaged in some multiverse adventures of his own, albeit off-screen. Since he's an older and more experienced Superman, it's not impossible that Clark traveled to other Earths and perhaps even met other versions of himself before moving his family to Smallville in the series premiere. Whatever these experiences were, they could become relevant later on if Superman and the others cross paths with more doppelgangers in Superman & Lois season 3 and beyond.