This quote is relevant:
The problem for Epic — and, I suppose, for me — is that to this observer it seems exceedingly likely that Apple is going to win this case, last night’s decision notwithstanding. Current Supreme Court jurisprudence is very clear that businesses — including monopolies — have no duty to deal with third parties, and if they do choose to deal with them (or are even compelled to), that they can choose the terms on which to do so. The only exceptions are if the monopoly in question changes the rules in an unprofitable way with the express purpose of driving out a competitor, or if any company — not even a monopoly — changes access to after-market parts and services.
Current US antitrust law does not favor Epic in this matter. Of Epic's ten claims, their strongest claim is probably the one tying in-app payment processing to app distribution services, but even that one is far from a slam dunk. And even if they were to succeed on that particular claim, the likely outcome would be that they would get to keep their payment system in Fortnite, not that they would be able to run their own app store.
I think people need to temper their expectations unless the laws change in the years it takes for this case to make it through the courts. A court ruling that Apple must allow third-party in-app payment systems is a somewhat realistic outcome, whereas a court ruling that Apple must permit third-parties to run their own app stores is probably a non-starter.