https://www.themarysue.com/michael-rosenbaum-please-play-lex-luthor-again/

Rosenbaum debunked a false report on Twitter that he was joining Crisis on Infinite Earths, and even tagged Jon Cryer, who plays Supergirl's Lex Luthor. "I think they’d be nuts not to," Cryer responded. "But I don’t know anything that you don’t." Rosenbaum responded to Cryer: "Cryer, stop being so lovable. I swear to God."

Smallville's Michael Rosenbaum: I turned down reprising Lex Luthor on Arrowverse's "Crisis on Infinite Earths" crossover (https://tvline.com/2019/09/24/arrow-crossover-michael-rosenbaum-smallville-lex-luthor/)

“Friends, many of you have tweeted and asked me about joining the Infinite crossover," Rosenbaum tweeted (https://twitter.com/michaelrosenbum/status/1176526751461019648) this morning. “I can’t tell you how much this means to me. I’ll just be straight up about this. WB called my agents Friday afternoon when I was in Florida visiting my grandfather in a nursing home. Their offer: No script. No idea what I’m doing. No idea when I’m shooting. Basically no money. And the real kick in the ass: ‘We have to know now.’ My simple answer was ‘Pass.’ I think you can understand why. I hope this answers all of your questions.”