Apple lost their lawsuit. The district court judge ruled that the anti-steering restrictions are anticompetitive and violated California law and required Apple to offer third party payment options. The appeals court agreed and temporarily paused part of that ruling to allow for appeal to the Supreme Court.
After all the legal process is done (even if Apple is not ruled a monopoly), Fortnite will be back on App Store (if Epic Games chooses to) and with its own payment system! That's the exact violation for which Apple removed them in the first place! The whole point was about how much Apple can charge app purchases and the courts basically said 0% if the developers choose so.
Apple didn't, by any reasonable interpretation, lose its case against Epic. It lost on one count and may have to make a minor change to its policies. But it won on the antitrust counts that really mattered, it won on its counterclaim, and it won when it came to the pivotal legal determination - i.e., is iOS app distribution (or some similiarly defined market) in itself a relevant antitrust market.
Epic didn't get what it wanted. It wanted to be able to put its own app store in Apple's App Store and sell apps through that app store. It didn't even get alternative in-app payment options. All it got was the ability for developers to direct users out of apps to alternative payment options. Such payment options already existed and were used quite extensively by some developers. It's just that developers may soon be able to tell people about those options in their apps. Apple would (for understandable reasons) prefer that not be the case, but it's not nearly as problematic as the other possibilities Apple faced through the case.
Further, Epic's ability to take advantage of the minor victory it had is limited because Apple won on the contract breach issue. The courts determined that Apple was justified in terminating Epic's developer account and now it's Apple's choice - not Epic's choice, as you suggest - whether Fortnite is allowed back in the App Store.
Your last sentence is also incorrect. The courts said nothing of the sort, even implicitly. They actually acknowledged the opposite. IP-compensation is a procompetitive rationale. The courts explicitly recognized that, even if Apple had been ordered to allow alternative IAP options, it would still be entitled to its 30% commission. This is one of the reasons Epic lost some aspects of the case. It failed to demonstrate a least restrictive means by which Apple could achieve its legitimate business goal of collecting compensation for the use of its IP.
With purchases made outside of apps - and payments not processed by Apple - Apple may (to avoid illegal tying concerns) need to reduce its commission some (e.g., to account for the cost of payment processing), but it will still be entitled to collect a commission for the use of its IP. Collecting that commission will just be more cumbersome and some parties may try to conceal what they really owe.
I'm happy to delve further into what the courts actually said on this issue, and what that means for Apple, if you're interested. But Apple's right to collect a commission was never really in jeopardy in this case.
- Apple removed Fortnite for adding its own payment option. The courts said Apple must allow apps to do that. It was an unequivocal and devastating loss for Apple.
- The courts said Apple violated California Unfair Competition Law (UCL), which prohibits far more behavior than the federal antitrust laws. It doesn't matter if Apple is a monopoly or not. California courts have interpreted UCL rather broadly and the Supreme Court is unlikely to disturb that interpretation. Apple will lose their appeal.
As to 1, the courts have not said that Apple must allow apps to do what Fortnite did. Fortnite, as you indicate, added an alternate IAP option. Apple still doesn't have to allow that; the courts were explicit on that point. What Apple has to allow is for developers to, within their apps, direct users to outside payment options.
As to 2, I'd agree that the Supreme Court is likely to decline Apple's cert petition. But it wouldn't need to disturb California's interpretation of its UCL in order to (grant the cert petition) and rule in Apple's favor. There are other significant legal questions involved and Apple isn't even asking the Supreme Court to overturn the lower courts as regards their interpretations of the Californial UCL or its application to Apple's policies.