With Harley Quinn Season 4 now concluded, it became clear the series was embracing its kooky roots more than ever. The Harley Quinn comics have done this a lot, delving into the Multiverse and such. Given that, Season 4 did a bit of world-hopping and actually explored alternate realities.
Source:https://www.cbr.com/harley-quinn-season4-unanswered-questions/