Earlier quoted context omitted.
Apple stores only sells accessories to their manufactured products, and isn't a retail platform. If Apple opened stores that sold a wide range a goods, including from other sellers, and then banned Dell, then yes, your hypothetical would be anticompetitive.
Then why aren’t apps an “accessory” to the iPhone where Apple can decide not to allow certain apps - including hypothetically Amazon? Do the console makers have a right to deny certain games on their platform? Does a physical store have to sell every product imaginable?
Apps are not accessories to hardware, and splitting hairs on the semantics is kind of banal.
Are you aware of what sea-lioning is?