MacOS – Apple’s iOS 14 Translate app on macOS

At the moment, you can't really do this. Although I suspect that Apple is looking to integrate iOS and macOS in the future so that this sort of thing can be done (purely speculation).

GarageBand on the Mac is different from the iPad version (it's more comprehensive) and it has been available on macOS for far longer than on iOS.

It is possible to run iOS apps in the Simulator app that comes with Xcode. However, it's not as simple as downloading an app from the App Store. You'd have to get the source code for the app, compile it in Xcode and run in the Simulator. Most apps being closed source, this won’t be possible!

It is possible to debug iOS apps on an iPhone wirelessly over WiFi, yes. This is a supported way of debugging in Xcode.

With Xamarin you can also debug over WiFi if you enable "Debug over WiFi" in the "iOS Debug" Build settings. However with Xamarin you need to launch the application over the USB cable. So you cannot do a fully wireless setup there.

Doing wireless debugging with a "cloud Mac" would probably require setting up a VPN connection or similar that makes it appear as though the cloud Mac is on your LAN. And it would only work with Xcode - not Xamarin.

A different approach would be to buy for example the Eltima USB Network Gate. Connect the iPhone to your local PC and use the software to connect that USB port over the network to your "cloud Mac" where it would appear as though the iPhone was physically connected. This should (at least in theory) allow you to launch and debug apps using Xamarin.