In the case of Apple, it's the same market. Because the only way to get access to the App Store is through an iPhone bought from Apple. And the only way to run an iOS app is with the same iPhone.

Yes, but this is only because Apple designed the phone that way. Apple should not be immune from antitrust law purely because they decided not to allow competition.

They do allow competition. Build your own phone and your own app store.

That's like saying that everything in the US is legal, since you're perfectly able to renounce your citizenship and move to Somalia where there aren't any laws.

So by that argument if MS would have disallowed installation of any other browser it would have been OK, because competitor could just build their own operating system.

The whole argument is that Apple is leveraging the position in one market (hardware) to gain advantage in another market. Your answer is "competitors can always build their own hardware" don't you see that this is a nonsensical argument?

If it was from the start, yes. Just like they don’t support replacin explorer.exe, the network stack. If you allow competition, but use leverage to stiffle it, it’s bad.

sigh That's not what I meant.

Apple decided where the boundary of competition lies by deciding to bundle their phone, their operating system, their app store, and their code signing policies into a package deal. A thicket of copyright laws forbid you from unbundling any combination of these. For example, I can't legally run iOS on my Pixel 8 Pro. It is legal to run Android on an iPhone, except the hardware boot ROM is designed to reject anything not signed by Apple, and Apple won't sign Android. You can circumvent that by taking advantage of security vulnerabilities in the boot ROM[0], and that's legal, too, but you can't legally tell anyone about those vulnerabilities because telling people how to break copy protection is a felony.

This same logic applies to application software. It's legal to jailbreak[1] your phone to install non-App-Store apps, but illegal to provide the jailbreak tool necessary to install those apps. If Epic had decided to release a jailbreak to install the Epic Games Store, instead of releasing a hotfix for third-party in-app billing and suing for antitrust, Tim Sweeney would have been thrown in jail for violating 17 USC 1201.

In copyright law, there's a concept of copyright misuse, which is what the courts call using copyright to break antitrust law. Copyright allows you monopoly control over your work, but you are not allowed to use that control to maintain an illegal monopoly that's outside of the copyright bargain. In other words, you don't get to opt-out of forms of competition you don't like. Congress decides those.

So no, "build your own phone and app store" is not enough. And letting Apple dictate the conduct of their competitors is effectively giving them antitrust immunity.

[0] Which are, BTW, once-in-a-decade. We've had a grand total of two bugs that can be used to install alternative operating systems on an iPhone.

[1] Jailbreak bugs aren't as scarce as boot ROM bugs, but they've been getting scarcer over time. This is not because Apple is doing a good security job, but because the NSA is hoarding all the good bugs for themselves.

Hmm making the argument that apple has a monopoly on the phone market is not easy though.

I my opinion the two markets are: Providing apps on iPhone, and offering payment processing for apps on iPhone. Apple is using its absolute monopoly on providing apps to also entrenched itself in the market of providing payment for apps.