No fan of apple. Don't own a single product.
But my guess they are planning to argue thay this part of the rule.
"at prices or conditions that are different from those offered through the online intermediation services of the gatekeeper."
Mean they cannot allow free side loading when many apps on their store have to pay to be available. Also as they have rules limiting the apps allowed via their store front. Allowing free side loading without checking the activities of the app. Would also be allowing conditions different from their store.
My guess is they want to argue that the law is badly formed and cannot be followed while providing a safe enviroment within your own services.