It looks like Xcode 16 beta 5 and Xcode 16.1 beta don’t work with a Swift 6 project anymore due to false concurrency errors, while Xcode 16 beta 4 works fine. Getting errors like:

Main actor-isolated property ‘label’ can not be referenced from a nonisolated context

To test, I started from the default “Game” project template with SpriteKit and changed to GameScene.swift file to something simple like this:

// GameScene.swift
import SpriteKit
import GameplayKit

class GameScene: SKScene {  // GameScene is @MainActor as a subclass of SKNode
    
    var label : SKLabelNode = SKLabelNode(text: "Initial text")
    override func didMove(to view: SKView) {
        addChild(label)
    }
}

@MainActor final class State: GKState {
    
    unowned private let scene: GameScene
    
    init(scene: GameScene) {
        self.scene = scene
    }
    
    override func didEnter(from previousState: GKState?) {
        scene.label.text = "Entered State"  // Main actor-isolated property 'label' can not be referenced from a nonisolated context
                                            // Main actor-isolated property 'text' can not be mutated from a nonisolated context
    }
}

It seems that the @MainActor tag on the class State is not working for methods that were overridden. This is most likely because GKState is not marked so its methods are nonisolated. But what is the solution in this case?