Claude31, thank you for your reply. However, I can see that Xcode 12 uses @main entry point and not @UIApplicationMain in AppDelegate. Basically, what I'm saying is, as a newbie, I haven't a clue where to learn about app architecture. Is there someone who can point me to a good resource on Apple's Documentation. I don't think something like this should be hidden. It should be made obvious to anyone coming to Apple's Documentation site for the first time, don't you think?

Claude, thanks for your reply. To answer your question, no I'm not using SwiftUI. I'm selecting Storyboard but I still see @main. I think I found my answer in the Swift Language Reference but I'm still baffled by the app architecture. I guess I'll simply have to go ahead and work my way through "Start Developing An iOS App" and see where that leads me. Thanks again Claude.