Example code of a simple integration between SwiftUI and SpriteKit using the delegate pattern.

SquareGame-After.swift

import SwiftUI
import SpriteKit

protocol SquareGameLogicDelegate {
    var totalScore: Int { get }
    
    mutating func addPoint() -> Void
}

// 1. Conform the ContentView to the SquareLogicDelegate protocol
struct ContentView: View, SquareGameLogicDelegate {
    // 2. Implement the totalScore variable and add the @State property wrapper
    // so once it changes value the user interface updates too
    @State var totalScore: Int = 0

    mutating func addPoint() {
        self.totalScore += 1
    }
	
    var screenWidth: CGFloat { UIScreen.main.bounds.width }
    var screenHeight: CGFloat { UIScreen.main.bounds.height }

    var gameSceneWidth: CGFloat { screenWidth }
    var gameSceneHeight: CGFloat { screenHeight - 100 }
    
    var squareGameGameScene: SquareGameGameScene {
        let scene = SquareGameGameScene()
        
        scene.size = CGSize(width: gameSceneWidth, height: gameSceneHeight)
        scene.scaleMode = .fill
        
	// 3. Remember to assign your view as the gameLogicDelegate of your game scene
        scene.gameLogicDelegate = self
	    
        return scene
    }
    
    var body: some View {
        ZStack(alignment: .top) {
            SpriteView(scene: self.squareGameGameScene)
                .frame(width: gameSceneWidth, height: gameSceneHeight)

	    // 4. An use the totalScore property to show the updated score
            Text("Score: \(self.totalScore)")
                .font(.headline).fontWeight(.bold)
                .padding().background(Color.white).cornerRadius(10)
                .overlay(RoundedRectangle(cornerRadius: 10).stroke(lineWidth: 4.0))
        }
    }
}

struct GameSizes {
    static let squareSize: CGFloat = 40.0
}

class SquareGameGameScene: SKScene {
    var gameLogicDelegate: SquareGameLogicDelegate? = nil
	
    private var lastTimeSpawnedSquare: TimeInterval = 0.0
    
    override func didMove(to view: SKView) {
        self.setUpGame()
    }

    override func update(_ currentTime: TimeInterval) {
        if self.lastTimeSpawnedSquare == 0.0 { self.lastTimeSpawnedSquare = currentTime }
        let timePassed = currentTime - self.lastTimeSpawnedSquare

        if timePassed >= 2 {
            self.spawnNewSquare()
            self.lastTimeSpawnedSquare = currentTime
        }
    }

}

// MARK: - Setting up the game
extension SquareGameGameScene {
    private func setUpGame() {
        backgroundColor = SKColor.white
    }
}

// MARK: - Handling Interaction
extension SquareGameGameScene {
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        
        let touchPosition = touch.location(in: self)
        
        if let selectedNode = nodes(at: touchPosition).first as? SKShapeNode {
            self.destroy(selectedNode)
            self.addPoint()
        }
    }
    
}

// MARK: - Square Creation Dynamics
extension SquareGameGameScene {
	
    private func spawnNewSquare() {
        let square = self.getNewSquare()
        square.position = self.getRandomPosition()
        
        addChild(square)
    }
    
    private func getRandomPosition() -> CGPoint {
        let screeWidth = self.frame.width
        let screeHeight = self.frame.height
        
        let minX = 0 + (GameSizes.squareSize * 2)
        let maxX = screeWidth - (GameSizes.squareSize * 2)
        
        let minY = 0 + (GameSizes.squareSize * 2)
        let maxY = screeHeight - (GameSizes.squareSize * 2)
        
        let randomX = CGFloat.random(in: minX...maxX)
        let randomY = CGFloat.random(in: minY...maxY)
        
        return CGPoint(x: randomX, y: randomY)
    }
    
    private func getNewSquare() -> SKShapeNode {
        let newSquare = SKShapeNode(rectOf: CGSize(width: GameSizes.squareSize, height: GameSizes.squareSize))
        newSquare.fillColor = SKColor.red
        newSquare.strokeColor = SKColor.black
        newSquare.lineWidth = 4.0
        
        return newSquare
    }
    
}

// MARK: - Square Destruction Dynamics
extension SquareGameGameScene {
    private func destroy(_ square: SKShapeNode) {
        square.removeFromParent()
    }
}

// MARK: - Score Dynamics
extension SquareGameGameScene {
    private func addPoint() {
        if var gameLogicDelegate = self.gameLogicDelegate {
            gameLogicDelegate.addPoint()
        }
    }
}

SquareGame-Before.swift

import SwiftUI
// Import SpriteKit to have access to the SpriteView(_:) View
import SpriteKit

struct ContentView: View {
    // Getting the dimensions of the screen
    var screenWidth: CGFloat { UIScreen.main.bounds.width }
    var screenHeight: CGFloat { UIScreen.main.bounds.height }

    // Set the dimensions of the game scene
    var gameSceneWidth: CGFloat { screenWidth }
    var gameSceneHeight: CGFloat { screenHeight - 100 }
    
    // Initialize the Game Scene
    var squareGameGameScene: SquareGameGameScene {
        let scene = SquareGameGameScene()
        
        scene.size = CGSize(width: gameSceneWidth, height: gameSceneHeight)
        scene.scaleMode = .fill
        
        return scene
    }
    
    var body: some View {
		// You can also use a VStack to organize your user interface
        ZStack(alignment: .top) {
            // Use the SpriteView from SpriteKit frameworks to present
            // your game scene
            SpriteView(scene: self.squareGameGameScene)
                .frame(width: gameSceneWidth, height: gameSceneHeight)
            // Presents the score of the player
            Text("Score: \(0)")
                .font(.headline).fontWeight(.bold)
                .padding().background(Color.white).cornerRadius(10)
                .overlay(RoundedRectangle(cornerRadius: 10).stroke(lineWidth: 4.0))
        }
    }
}

import SpriteKit

// A struct to store values that repeat often in the code
struct GameSizes {
    static let squareSize: CGFloat = 40.0
}

class SquareGameGameScene: SKScene {
    // 1. A variable to keep track of how much time since the last update cycle
    private var lastTimeSpawnedSquare: TimeInterval = 0.0
    
	// 2. Set up the game once the Game Scene is presented
    override func didMove(to view: SKView) {
        self.setUpGame()
    }

    override func update(_ currentTime: TimeInterval) {
        // 3. Every 2 seconds a new square is created and placed on the screen
        if self.lastTimeSpawnedSquare == 0.0 { self.lastTimeSpawnedSquare = currentTime }
        let timePassed = currentTime - self.lastTimeSpawnedSquare

        if timePassed >= 2 {
            self.spawnNewSquare()
            // Reseting the timer
            self.lastTimeSpawnedSquare = currentTime
        }
    }

}

// MARK: - Setting up the game
extension SquareGameGameScene {
    private func setUpGame() {
        backgroundColor = SKColor.white
    }
}

// MARK: - Handling Interaction
extension SquareGameGameScene {

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
		// Gets the first touch object in the set of touches
        guard let touch = touches.first else { return }
        // Gets the position of the touch in the game scene
        let touchPosition = touch.location(in: self)

        // 1. Checks if there is a SKShapeNode where the player touched.
        if let selectedNode = nodes(at: touchPosition).first as? SKShapeNode {
			// 2. If so, calls a function to destroy the node
            self.destroy(selectedNode)
        }
    }
    
}

// MARK: - Square Creation Dynamics
extension SquareGameGameScene {
    
	// Called every two seconds in the update(:_) function.
    private func spawnNewSquare() {
        let square = self.getNewSquare()
        square.position = self.getRandomPosition()
        
        addChild(square)
    }
    
	// Returns a random position based on the dimensions of the game scene
	// and the dimensions of the squares.
    private func getRandomPosition() -> CGPoint {
        let screeWidth = self.frame.width
        let screeHeight = self.frame.height
        
        let minX = 0 + (GameSizes.squareSize * 2)
        let maxX = screeWidth - (GameSizes.squareSize * 2)
        
        let minY = 0 + (GameSizes.squareSize * 2)
        let maxY = screeHeight - (GameSizes.squareSize * 2)
        
        let randomX = CGFloat.random(in: minX...maxX)
        let randomY = CGFloat.random(in: minY...maxY)
        
        return CGPoint(x: randomX, y: randomY)
    }
    
	// Creates a SKShapeNode to be used in the game.
    private func getNewSquare() -> SKShapeNode {
        let newSquare = SKShapeNode(rectOf: CGSize(width: GameSizes.squareSize, height: GameSizes.squareSize))
        newSquare.fillColor = SKColor.red
        newSquare.strokeColor = SKColor.black
        newSquare.lineWidth = 4.0
        
        return newSquare
    }
    
}

// MARK: - Square Destruction Dynamics
extension SquareGameGameScene {
    private func destroy(_ square: SKShapeNode) {
        square.removeFromParent()
    }
}