Well...I would say it seems the latest JL run basically hyping up the Brothers Three to be the greatest powers in the DC Multiverse (other than Perpetua and perhaps Mxy), and the World Forger has shown both Multiversal + durability and Multiversal/Trans-Multiversal feats of fashioning/governing the laws and substance of reality. I mean...the guy literally kept a multiverse-busting God (Barbatos) as a pet on his shoulder for billions of years.
Comparatively, True Form Darkseid was collapsing the mainstream multiverse beneath the Sphere of the Gods into one reality by falling into it. With the ALE, a truly Multiversal/Multiversal+ power, Darkseid would be in command of megaversal strength. I’m not sure if collapsing the multiverse beneath the Sphere of the Gods is enough to match the World Forger, but with the ALE it would be pretty hard to say who wins decisively.
Spoiler:
Gun to my head, I would say World Forger.