I don't understand this argument. All software, by definition, "dictates" how a device works. If you buy an app, you don't get to decide how it works. You don't like it? Don't buy it. I don't see a big push for people crying to the government to stop Activision from dictating how to play Call of Duty.

Apple doesn't dictate what software runs on your iPhone, any more than a toaster manufacturer dictates whether you can use it as a space heater, or Toyota dictating whether your car can function as a boat, or Epic Games dictating whether Fortnite can be used to prepare your taxes.

No, Apple isn't going make the process of running your own software easy, but you are legally entitled to break whatever barriers you like and replace the OS with a Linux distro. No, you shouldn't be legally entitled to force Apple to make their operating system do whatever random thing you want it to.