Open the project in Xcode 13. Select the project file. In the file inspector on the right side of the window is a Project Format menu. Choose an earlier version of Xcode from that menu to open the project in earlier Xcode versions.

The keyword you're looking for is #available. Use an if-else block, not #if and #endif, putting the iOS 14 code in the else part of the block. TextField("Username", text: $username) if #available(iOS 15.0, *) { .focused($focusedField, equals: .username) } else { // Put the iOS 14 equivalent code here. }

If you want someone to help you, you need to provide more details on what you are doing, such as the type of project you're creating. What SDK do you want to remove? What kind of program are you trying to make? If you want to start from 0 in Xcode, create an empty project. Click Other at the top of the New Project Assistant to access the empty project template.

You need a Mac that can run the latest version of macOS to submit apps to the App Store. The following page from Apple lists the Macs that can run the latest version of macOS: Mac Hardware Requirements

The following article has a collection of resources for learning Mac development: swiftdevjournal.com/resources-for-learning-mac-development/ Regarding learning SwiftUI or AppKit, you're going to find many more recent articles and tutorials on SwiftUI. Most of these articles are focused on iOS, but most of the material will apply to Mac too. Lists are the one view where you'll run into issues because lists(table views) have much different behavior on Mac than on iOS.

If you want someone to help you, you need to be much more specific about what you are doing, what you expect to happen, and what happens. Does the class of the view controller in the storyboard match the name of the class in the source code file where you are trying to create the outlet? Forgetting to set the view controller's class in the storyboard is a common reason for being unable to connect and create outlets and actions.

If you search for put Xcode project on GitHub in a search engine, you will find many articles on setting up git with Xcode, including the following: swiftdevjournal.com/putting-your-xcode-project-on-github-bitbucket-or-gitlab/