Many, but far from all, otherwise mobile-only applications are available on the Mac App Store for Macs with an Apple silicon processor. Such Macs can hypothetically run any iPhone or iPad application, though individual developers can choose whether or not to offer that functionality. There are multiple reasons why a company might not offer their iPhone app on Mac—maybe they don't want to optimize it for a bigger display, maybe it's broken in some way, or maybe they just aren't interested in supporting another platform.
You might disagree with that decision, though, and wondering whether it's possible to use those apps on your Mac anyway. And it is, sort of: PlayCover is an app capable of running any iPhone application you can think of, at least in theory. The problem is, there's no straightforward way to get versions of the applications that will work with it.
The iOS encryption problem
Apple encrypts the applications offered in the App Store, meaning you can't just download and install them directly—you have to go through the storefront. The main workaround requires you to jailbreak an iPhone and use software designed to decrypt applications. In this way, you can create .ips files from the apps you've downloaded or purchased that you can open in PlayCover.
You could also, in theory, download the .ips files from a third party—there are a few websites out there that offer them. The issue there is that this method requires trusting software from internet strangers that you're then installing on your computer, which is hard to recommend for a bunch of security reasons. (You never know what malicious software may be hidden in those files.) There's also the question of piracy, as these sites let you bypass the App Store encryption, which is typically a violation of the Digital Millennium Copyright Act.
PlayCover works, to a point
With all of these caveats in mind, I did manage to get the iPhone version of Duolingo running on my Mac. This is ideal, because the web version is missing all kinds of features, but it still isn't a like for like experience, as I won't get automatic updates like I would on an actual iPhone.
Beyond Duolingo, a few other iPhone applications and games I tried to open on my Mac either wouldn't launch, or couldn't reach the login screen. And because the games you're playing are effectively outside the Apple ecosystem, you won't have access to any of your in-app purchases, or even the ability to make new ones. It's an imperfect solution in many ways, with one main upside—running software you otherwise couldn't—and lots of potential downsides.
All of these points aside, I have to say that PlayCover has some clever features built in that allow you to control games optimized for touch. You can use your keyboard to emulate a gamepad, for example, making it possible to play supported games using your keyboard. If that doesn't work, you can assign keys to simulate screen taps, so your key presses select the corresponding on-screen buttons to control games. It takes a little bit of work on your part, but it makes it possible to play games designed for a touchscreen using keyboards.
Thanks to Apple silicon, the iPhone, iPad, and Mac truly are related platforms. There's nothing stopping you from running any iPhone application on your Mac, at least in theory. But for most people, it's probably a good idea to stick to the iPad applications you can find in the Mac App Store.
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