FYI: Playing a movie using AVPlayer in Big Sur

took a bit of experimenting...

1. import AVKit    //  macOS & iOS

5. class ViewController_myShow: NSViewController {

7.     

9.     @IBOutlet var myMOV: AVPlayerView!

10.

1.     

3.     override func viewDidLoad() {

5.         super.viewDidLoad()

7.         

9.         let playerView = AVPlayerView()

20.
21.         playerView.translatesAutoresizingMaskIntoConstraints = false
22.
23.         view.addSubview(playerView)
24.
25.
26.
27.         playerView.leadingAnchor.constraint  (equalTo: view.safeAreaLayoutGuide.leadingAnchor ).isActive = true
28.
29.         playerView.trailingAnchor.constraint (equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true
30.
31.         playerView.topAnchor.constraint      (equalTo: view.safeAreaLayoutGuide.topAnchor     ).isActive = true
32.
33.         playerView.bottomAnchor.constraint   (equalTo: view.safeAreaLayoutGuide.bottomAnchor  ).isActive = true
34.
35.
36.
37.         playerView.controlsStyle = .floating
38.
39.         playerView.showsFrameSteppingButtons   = true
40.
41.         playerView.showsFullScreenToggleButton = true
42.
43.         
44.
45.         guard let path = Bundle.main.url(forResource: "myMovie", withExtension: "mov") else { return }
46.
47.
48.
49.         let player = AVPlayer(url: path)
50.
51.             playerView.player = player
52.
53.         playerView.player?.play()  
54.
55.     }
56.
57. }

The StoryBoard:AttributesInspector:AVPlayerView settings don't work for me... exactly. I had to set StoryBoard:AttributesInspector:AVPlayerView:ControlsStyle:none then include lines 37-41 in my code.
The default is StoryBoard:AttributesInspector:AVPlayerView:ControlsStyle:inline which appears on screen but does nothing, i.e., no control.
Line 21 is also required to be false.
The .mov file can be File:AddFilesTo 'd or copied to Assets.xcassets

see also:
Developer Forum:
"can't get extremely simple macOS video player to work..."

https://developer.apple.com/documentation/avfoundation/media_playback_and_selection/creating_a_basic_video_player_macos

Code Block 
			

import AVKit    //  macOS & iOS

class ViewController_myProduction: NSViewController {
    
    @IBOutlet var myMOV: AVPlayerView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let playerView = AVPlayerView()
        playerView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(playerView)

        if #available(macOS 11.0, *) {
            playerView.leadingAnchor.constraint  (equalTo: view.safeAreaLayoutGuide.leadingAnchor ).isActive = true
            playerView.trailingAnchor.constraint (equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true
            playerView.topAnchor.constraint      (equalTo: view.safeAreaLayoutGuide.topAnchor     ).isActive = true
            playerView.bottomAnchor.constraint   (equalTo: view.safeAreaLayoutGuide.bottomAnchor  ).isActive = true
        } else {
            // Fallback on earlier versions
        }

        playerView.controlsStyle = .floating
        playerView.showsFrameSteppingButtons   = true
        playerView.showsFullScreenToggleButton = true
        
        guard let path = Bundle.main.url(forResource: "myProduction", withExtension: "mov") else { return }

        let player = AVPlayer(url: path)
            playerView.player = player
        playerView.player?.play()  
    }
}