> their monopoly on their hardware

This way of viewing things leads to some really silly conclusions. Apple doesn't have a monopoly on the iPhone, the premise is intrinsically absurd. By this argument literally any non-commodity product is a "monopoly" of the company that distributes it.

Moreover, what Apple sells isn't hardware, it's hardware with software on it. That's the product. As far as I know there is no official way to buy either iOS or an iPhone that doesn't have iOS installed. Sometimes companies take an opinionated stance on how they distribute their products, like a firearm manufacturer that only manufactures firearms that have a safety. Framing that sort of thing as an antitrust issue is unreasonable.

Monopoly is indeed not technically the right term, but it's not necessarily a monopoly itself that causes antitrust issues, it's the business practices that are enabled by it. A large player in a market that uses business practices to capture and hold more of that market by erecting barriers of entry are definitely sailing into antitrust waters.

In essence, any practice that helps compete in the market by other ways than increasing value to the consumer is suspect. Incidentally, this is a double edges sword, as this is the interpretation of the antitrust laws that has enabled the rise of so many monopoly-like companies in the last few decades. (e.g. Amazon: we're increasing value to customers because we can offer lower prices if we're larger)