Per on in-app purchases, Apple has added the following bullet point:
Apps offering “loot boxes” or other mechanisms that provide randomized virtual items for purchase must disclose the odds of receiving each type of item to customers prior to purchase.
Basically, the App Store now operates on the same level of some Asian countries which have laws on the books about loot box (or gacha) mechanics. If you're buying something random, you need to know your chances of getting things. Historically, Apple's policies have favored consumers, and forcing developers to show that the cool hat you really want out of that loot crate only has a 0.001% chance of being there when you open it is pretty consumer friendly.
It'll be interesting to see what if any impact this has on the popularity of gacha mechanics in mobile games. Scratch off lottery tickets have the odds printed on all of them, and it doesn't seem to stop anyone from buying them. I suspect this will be the same. Regardless, once Apple starts enforcing this new policy, I'm sure it will be eye opening to see just how rare getting anything good in games that lean on this style of monetization actually is.