Apple's new legal case takes issue with specific decisions taken by the European Commission under the DMA, but the exact details of the challenge have not yet been publicized. The case is expected to include an argument against the ‌App Store‌ being included on the EU's list of gatekeeper platforms, which requires app sideloading to be an option to allow users to avoid the ‌App Store‌ if they wish.

This is not correct. Apple has so far not disputed iOS being classed as a core platform service. This means they are not disputing the requirement to open up iOS for competing app stores. However they have disputes the App Store becoming a core platform service. This would place additional requirements on the App Store around which applications they accept and decline, prominence of their own applications relative to competitors, and a host of others like marketing transparency.

This is Apple throwing as much as they can at the wall to see what sticks.