When deploying the ARKit Sample project from https://developer.xamarin.com/samples/monotouch/ios11/ARKitSample/, I get the build error Invalid architecture: ARMv7. 32-bit architectures are not supported when deployment target is 11 or later
.
Everything with the deployment device and my development machine checks out:
I am running iOS 11 on the deployment device (an iPhone 6S Plus - ARKit will not run in the emulator), and have Xcode 9 installed (and have launched it once before starting Visual Studio for Mac). Visual Studio for Mac has also been updated to the latest Stable release (ARKit is not available on the Alpha and Beta releases at this point in time).
I am posting the fix to this problem below, in the hopes that it helps others who are going to be developing with ARKit on iOS 11.