So, how would Superman & Lois tease that Captain Luthor is actually Alexander?
The Alexander Luthor Jr. of DC Comics gained the ability to control matter after surviving his Earth’s destruction, which he could use to create energy blasts and create portals.
The most obvious tease to me would be him tailing off an attack on Superman after seeing Lois or some reveal that he has superpowers beyond the intellect to create that fancy super suit.
Again, the Arrowverse can play fast and loose with characters, so there’s no guarantee the character can do anything like that, but if Captain Luthor does, that’s a dead giveaway in my eyes.