Xcode 12 - AppName's architectures (arm64) include none that iPhone 11 Pro can execute (Intel 64-bit)

You can simply remove VALID_ARCHS, then it works.

Adding all architectures (x86_64 armv7s arm64) to VALID_ARCHS works. Didn't analyse more, just worked.

I fixed the issue with the instruction on this page: https://medium.com/@khushwanttanwar/xcode-12-compilation-errors-while-running-with-ios-14-simulators-5731c91326e9

In the project file (.pbxproj) I excluded i386 and arm64 for all debug targets:

                EXCLUDED_ARCHS = "i386 arm64";

The change I made is only exclude them for simulator target:

                EXCLUDED_ARCHS = "";
                "EXCLUDED_ARCHS[sdk=iphonesimulator*]" = "arm64 i386";

The issue could be with the scheme. Go to Product > Scheme > Edit Scheme. Make sure that "Build Configuration" is set to "Debug" and not "Release"