I would recommend looking up what antitrust does and does not cover. This is not suitable grounds for antitrust arguments as the law is currently given; if you were arguing 'Apple has a monopoly on Apple-exclusive apps', you might have a case, but even then there are many apps that are cross platform, and those that choose to develop exclusively for Apple are making a market decision that they may be liable for if the cost of production increases because of it.

I don't think you can argue platform monopoly here any more than you could argue, say, that Amazon has a monopoly on AWS-specific services. Since an app developer can choose which platform to use with approximate levels of parity between those platforms and a few distinctive services per platform, it is my opinion that the 'platform monopoly' argument is rendered void. This argument is only weakened in recent years as feature parity increases between Android and Apple ecosystems.