问题：

新建工程，选择最低支持iOS13报错：

'main()' is only available in iOS 14.0 or newer

'Scene' is only available in iOS 14.0 or newer

'WindowGroup' is only available in iOS 14.0 or newer

解决：

注释掉上面代码，重新创建一个AppDelegate作为入口：

import Foundation
import SwiftUI

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // 创建一个UIHostingController来托管你的ContentView
        let contentView = ContentView()

        // 设置window
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.backgroundColor = .white
        window.rootViewController = UIHostingController(rootView: contentView)
        self.window = window
        window.makeKeyAndVisible()
        return true
    }
}

info.plist中移除Application Scene Manifest

然后，重新运行就没问题了