[mtouch] The executable path in the app is in the Contents/MacOS subdirectory (just like for macOS apps)

tools/mtouch/Application.mtouch.cs

@@ -1012,6 +1012,10 @@ namespace Xamarin.Bundler {
 			get {
 				if (Embeddinator)
 					return Path.Combine (AppDirectory, "Frameworks", ExecutableName + ".framework", ExecutableName);
+
+				if (Platform == ApplePlatform.MacCatalyst)
+					return Path.Combine (AppDirectory, "Contents", "MacOS", ExecutableName);
+
 				return Path.Combine (AppDirectory, ExecutableName);
 			}
 		}