要在退出后停止播放AVPlayerViewController，您可以使用UIViewRepresentable协议的onDisappear回调来实现。在onDisappear回调中，您可以停止播放器并将其置为nil。

下面是一个示例代码，演示如何使用UIViewRepresentable来停止播放AVPlayerViewController：

import SwiftUI
import AVKit

struct PlayerView: UIViewRepresentable {
    @Binding var isPresented: Bool
    
    private let playerViewController = AVPlayerViewController()
    private var player: AVPlayer? = AVPlayer(url: URL(string: "https://example.com/video.mp4")!)
    
    func makeUIView(context: Context) -> UIView {
        playerViewController.player = player
        playerViewController.showsPlaybackControls = true
        playerViewController.videoGravity = .resizeAspectFill
        return playerViewController.view
    }
    
    func updateUIView(_ uiView: UIView, context: Context) {
        // No-op
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject {
        let parent: PlayerView
        
        init(_ parent: PlayerView) {
            self.parent = parent
            super.init()
        }
        
        @objc func playerDidFinishPlaying() {
            parent.isPresented = false
        }
    }
    
    func onDisappear(perform action: (() -> Void)? = nil) -> Self {
        let controller = playerViewController
        controller.player?.play()
        
        DispatchQueue.main.async {
            NotificationCenter.default.addObserver(
                controller.coordinator,
                selector: #selector(Coordinator.playerDidFinishPlaying),
                name: NSNotification.Name.AVPlayerItemDidPlayToEndTime,
                object: controller.player?.currentItem
            )
        }
        
        return self
    }
    
    func updateUIViewController(_ uiViewController: UIView, context: Context) {
        // No-op
    }
    
    func stopPlayer() {
        playerViewController.player?.pause()
        playerViewController.player = nil
    }
}

struct ContentView: View {
    @State private var isPlayerPresented = false
    
    var body: some View {
        VStack {
            Button(action: {
                self.isPlayerPresented.toggle()
            }) {
                Text("Play Video")
            }
        }
        .sheet(isPresented: $isPlayerPresented) {
            PlayerView(isPresented: self.$isPlayerPresented)
                .onDisappear {
                    self.isPlayerPresented = false
                    self.stopPlayer()
                }
        }
    }
    
    func stopPlayer() {
        NotificationCenter.default.post(name: NSNotification.Name.AVPlayerItemDidPlayToEndTime, object: nil)
    }
}

在上面的示例中，PlayerView是一个UIViewRepresentable，用于呈现AVPlayerViewController。在PlayerView的onDisappear回调中，我们添加了一个通知监听器来捕获播放器完成播放的事件。当播放完成时，我们将isPresented标志设置为false，以便关闭播放器。

在ContentView中，我们使用.sheet修饰符将PlayerView作为模态视图呈现。在PlayerView的onDisappear回调中，我们还调用了stopPlayer方法来停止播放器。

希望这可以帮助您解决问题！