Vesper Fairchild says Burt Ward's Robin's catchphrase: "Holy police state, Batwoman! Can we find her already?"
Luke says to Alice that Bruce knew someone who had a 'cryogenic tank' and they could put her in cryostasis - a shout out to popular Batman villain Mr. Freeze, who put his wife Nora Fries into a cryostasis tank to find a cure for her disease. His wife Nora also appears as an inmate in Arkham in "Elseworlds", and it's implied that at some point, Victor became a villain, as his cryogenic gun is seen briefly in Arkham, as well.
The episode doesn't specifically says that the person Bruce knew was Victor Fries; it's very possible that it was Batman who locked a now-villainous Victor in Arkham, prompting the brief reference in "Elseworlds", though it is also possible, with "Crisis" having made some alterations to Arrowverse's history with the creation of Earth-Prime, that he's still just a researcher, operating in a lab somewhere in Gotham City, his villain potential not yet realized. In either case, it's an interesting suggestion and lays the groundwork for the cold villain to potentially pop up in the future.