Not a final decision. SCOTUS (via Kagan) refused to overturn a stay on a decision while legal proceedings continue. Basically just an order to keep things as-is until the case finishes working its way through the courts.

Which as I understand it is generally how things work: if there's no clear likely winner, go with the interim situation that most easily can be rectified if it is later ruled to have been wrong. In this case, if the ruling goes against Apple than they can be ordered to give money to Epic and other app-owners based on the revenue brought in from them to Apple during the appropriate period. The opposite case would require more complex estimates (how much revenue was shifted away from Apple incorrectly, in the case where Apple wins) and further it'd result in unnecessary consumer friction: users would go from A to B then back to A again.