Summary of lawsuit.
Apple offers apps in its stores. Apple gets 15% of the revenue from sales of these apps as payment for dev tools, hardware development, hosting the store in the first place, and distribution, etc. These apps can have in-app purchases for subscriptions and microtransactions. Those in-app purchases are also subject to the 15% cut for Apple.
Epic didn't like that, so they redirected users, within the app itself, to a separate "external" link that bypassed Apple's payment system so that they didn't have to give up the 15% cut. This is against the ToS for hosting an app in the App Store.
Apple is COMPLETELY FINE with a company offering its in-app purchases and subscriptions through their own separate services (and obviously doesn't take a cut from that). Netflix, for example, can be subscribed to either on Netflix.com (and you log in through the app), or you can subscribe to Netflix directly in the app itself (where Apple gets a cut). Apple is NOT fine with developers bypassing its software system for handling transactions, so they kicked Epic out of the App Store for doing this.
Epic then actively pulled playback support for its apps on Apple's platforms (until then, the apps still worked fine as long as you had downloaded them already) and sued Apple for discrimination.
Summary of lawsuit ends.
That's what happened, physically. The discussion is whether Apple has the legal capability to do this, as well as on other topics, such as the acceptable extent of the "walled garden" approach to security, stability, and protection of user content against predatory business tracking. Never mind any double standards held in software deals regarding Apple (and
other companies) and Epic (and other companies).