But this year at WWDC 2020 the UIKit team introduced UICollectionLayoutListConfiguration, a modern API designed to replace UITableViews, but AppKit didn't get any of this love. This was a huge addition at WWDC 2019 last year, and AppKit got it's own version, NSCollectionViewCompositionalLayout, which had largely the same feature set as the UIKit version. Take UICollectionViewCompositionalLayout for example. AppKit actually served as the base for UIKit, but as iOS has enjoyed much more popularity than macOS in the recent years UIKit APIs have been largely refined and improved to be more modern, pleasant to work with and 'swifty', whilst AppKit's macOS APIs have remained largely unchanged. MacOS has a similar, but incompatible framework for UI creation, called AppKit. These are components built by Apple engineers and designed specifically to work on Apple's iOS and iPadOS devices (or at least that used to be the case until catalyst rolled around, but that's a story for another day). Since you're coming from iOS I assume you're familiar with UIKit - it's what gives you all the UI-prefixed classes like UIView, UIViewController, UICollectionViewCompositionalLayout and so on. UIKit and AppKit are the frameworks you use to interact with the app's UI on the device you're running on. I'm assuming your issue mostly has to do with migrating from UIKit to AppKit. What is different between the platforms are the frameworks they support. Swift as a language is the same on both iOS and macOS - there's no porting that you need to do to move logic between the two. Some kind of help document would be great to have. I'm just not versed enough in the Swift language to know what I need to do.

However, until that happens it seems different libraries have to be imported and different classes loaded in order to get something that works for iOS to work in macOS.

It appears Apple is trying to get to the point where one day it doesn't matter which platform you're targeting in Swift, the code will work on any of their platforms. So, I thought I would ask here to see if there is some kind of cross-walk that would show what one needs to do to convert swift iOS app/code to be compatible with macOS? I try running the examples and I get errors telling me various classes are unknown, which I guess means they aren't being imported into the macOS app. It seems the iOS world is so prolific that the macOS stuff is getting pushed down in the search engines. I am having a difficult time finding swift example code targeted for macOS development.

Swift code mac