App Kitで自動フルスクリーン

NSWindowのtoggleFullScreenメソッドを使う。

import Cocoa

class ViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidAppear() {
        super.viewDidAppear()

        view.window?.collectionBehavior = NSWindow.CollectionBehavior.fullScreenPrimary
        view.window?.toggleFullScreen(nil)
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }
}