Getting error build time "Cannot find type 'GADInterstitial' in scope" I guess GADInterstitial is not a type in a framework of Apple's. You should better find a better place to ask it to get better responses sooner. And better include more description of your environment and what you have done.

Have you tried using single-quotes? OTHER_SWIFT_FLAGS = "$(inherited) -D COCOAPODS -Xcc '-Wno-error=non-modular-include-in-framework-module'";

Apple Developer has mentioned that you can add 'UIUserInterfaceStyle' key to info.plist. But I checked there is no such key in list and it also gives error when you upload app to the App Store. What value have you set? Light? Some articles say it needs to be capitalized, not light.

Running/debugging apps on iOS 14.5+ devices is not supported with Xcode 12.4. https://developer.apple.com/forums/thread/679482?answerId=673429022#673429022 You should better prepare an upgraded Mac and try with Xcode 12.5.

When I enter it, It itself automatically switches to key called 'Appearance' When the raw key UIUserInterfaceStyle is shown as Appearance in human readable mode, that means UIUserInterfaceStyle is (at least, once was) the supported key. Appearance doesn't have Light / Dark or anything... For many values taking String value, the value would not be shown automatically. When I enter it is info.plist it doesn't get accepted... You have not clarified what you have entered on what key...

Is this a bug? and should I raise a bug with Apple for this ? Not sure if Apple would call this issue as bug. But if you have the project which can reproduce the same issue, you should better send a bug report to Apple.

I consider this a bug. bug? I have never heard of this sort of bugs found in Swift Standard Library. So, it is very likely a bug of your code. You may be doing something wrong from somewhere you have not shown yet. Or may be accessing the Array from multiple threads. Can you show a complete code which can reproduce the same issue?

I have entered 'UIUserInterfaceStyle' as a key but it automatically replaced by 'Appearance'... It is not a problem, it actually is held as UIUserInterfaceStyle internally. If you want to see the raw key, choose Raw Keys & Values on the context menu shown in the editor of Info.plist. If you are sure you set Light there and it causes error on archiving, or it has no effect for LaunchScreen.storyboard, please share your experience.

Is it possible to make, test, and publish an iOS/iPadOS app on Windows 10? NO. Using some hybrid frameworks, you can make and test (in limited range) an iOS/iPadOS app on Windows, but you cannot publish it unless you can use a Mac. So is there any alternative/port of Xcode on Windows?  NO.

The return type (id) is not good for bridging to Swift. Can't you give it an explicit return type? (NetworkManager *)sharedManager {

scope is an area meaning some range in code where each name is valid. Maybe you need some specific description to your issue. Please show enough code which represents what would be your issue.

The return value must conform to Shape. It's a fundamental requirement by function signature, isn't it?  NO.

The reason is? Already written. a value of a protocol type doesn’t conform to that protocol;

You mean, just treat it as a rule?  YES. It is not a description specific to this case, it is a general rule of protocol in Swift. The only exception I know is the protocol Error, which conforms to Error.

In fact, many developers are struggling with this characteristics of Swift protocols. If you have some interest in the future of Swift, forums.swift.org may be a good place to learn and discuss.