Because of an Easter egg in Supergirl, the groundwork has been laid for a major character from Smallville to appear on Superman & Lois. Chloe Sullivan, who was created specifically for the Superman prequel series before being adapted to the comic books, could cross paths with Clark (Tyler Hoechlin) and Lois (Elizabeth Tulloch). Chloe Sullivan - played on the series by disgraced actress Allison Mack - was the only character aside from Clark to appear in all ten seasons of Smallville.
Introduced as a high school classmate and one of his best friends, Chloe was a journalist and hacker who helped him through several of his biggest jams. Her resources and skills made her a valuable asset while he was in high school, and their connection grew stronger once she discovered the truth about his Kryptonian heritage. She protected both him and his secret, and even developed a presence in Smallville’s Justice League as their eyes and ears, “Watchtower.”
During a flashback sequence to Kara Danvers’ high school days in a season 3 episode, it was confirmed that the Arrowverse’s Superman had his own Chloe in his life. A young Kara was seen bringing up “Clark’s friend”, Chloe. Apparently, they needed some technical assistance while looking into a murder. Her last name wasn’t said, but there was no denying this was a Smallville reference since Kara also mentioned the Wall of Weird. When Clark and Chloe were in high school between season 1 and season 4 she had a Wall of Weird, where she kept track of all the strange occurrences in Smallville.
Based on Supergirl’s Chloe reference, it appears the Arrowverse’s Chloe helped Clark in a way that’s not unlike the role she held in Smallville's first four seasons. What happened to her after that is something that can be explored in Superman & Lois. The series could take this Easter egg and turn it into something much bigger by properly introducing the Arrowverse’s Chloe Sullivan, played by a new actress. As for what story the show might provide her, it’s possible she could still live in Smallville and will reconnect with Clark. Also, it may be that she, like her Smallville counterpart, is Lois’ cousin. Superman & Lois can dive into her friendship with Clark, and also explain if she knows his secret.
The actress who originally played Chloe is mired in a major criminal case, but that doesn’t necessarily mean her character can’t have a future beyond Smallville, especially since it would be a new performer portraying her. After all, she was his most important ally in the series, and it’s abundantly clear that Smallville has a big influence on Superman & Lois. Whether an official Arrowverse debut for Chloe Sullivan happens or not, adding her to the show is certainly possible, thanks to Supergirl. If she were to appear, it would be interesting to see if she too helped Clark fulfill his destiny and become Superman.