The relevant info here being:

In addition to updating its streaming music rules, Apple today also added games from retro game console emulator apps to the list of permitted software allowable under guideline 4.7. Guideline 4.7 permits apps to offer HTML5 mini apps and mini games, streaming games, chatbots, game emulators, and plug-ins.

Apps may offer certain software that is not embedded in the binary, specifically HTML5 mini apps and mini games, streaming games, chatbots, and plug-ins. Additionally, retro game console emulator apps can offer to download games. You are responsible for all such software offered in your app, including ensuring that such software complies with these Guidelines and all applicable laws.

Game emulators have managed to sneak onto the ‌App Store‌ several times over the years by using hidden functionality, but Apple has not explicitly permitted them until now. The rule change that allows for game emulators is worldwide, as is support for apps that offer mini apps and mini games.