SwiftUI + SpriteView = Gray screen

Xcode 13 beta 2, iOS 15 beta 2, the following code produces a gray screen (the SKScene GameScene.didMove(to:) never gets called):

import SwiftUI
import SpriteKit

// A simple game scene with falling boxes
class GameScene: SKScene {
    override func didMove(to view: SKView) {
        physicsBody = SKPhysicsBody(edgeLoopFrom: frame)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        let location = touch.location(in: self)
        let box = SKSpriteNode(color: SKColor.red, size: CGSize(width: 50, height: 50))
        box.position = location
        box.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 50, height: 50))
        addChild(box)
    }
}

// A sample SwiftUI creating a GameScene and sizing it at 300x400 points
struct ContentView: View {
    var scene: SKScene {
        let scene = GameScene()
        scene.size = CGSize(width: 300, height: 400)
        scene.scaleMode = .fill
        return scene
    }

    var body: some View {
        SpriteView(scene: scene)
            .frame(width: 300, height: 400)
            .ignoresSafeArea()
    }
}

I have no idea how to fix / workaround this issue.

Any thoughts?