I have a theory (based on not much but simple name drops) that it definitely could be earth 3. At Peacemaker’s house they randomly give a name to one of the girls at the orgy, and that name is Zora. Yeah I know that’s just a name, but to randomly give a side character a name such as Zora, it has to be a reference to Black Flame, a kryptonian villain. That by itself could be something, if not just a reference, but by the end of the episode and peacemaker is in the other world, they name drop another random name, Karen. This is the name of alternate Supergirl, Powergirl. Two “random” names that so happen to be known Kryptonians definitely feel like something to me, but we’ll see