They could obviously forbid apps to show ads and implement a powerful, default-enabled adblocker into Safari. But why would they? The outfall would likely see many important developers pull their apps at least temporarily. Of the Top 10 Downloaded Apps of 2021 (https://www.macrumors.com/2021/12/02/apple-most-downloaded-a...) only a single one doesn't have ads. This could be Pyrrhic victory for Apple. It would most likely also seal the deal on sideloading regulation.