Working in SpriteKit I moved away from Hudson's example of pixelating an image as it assumed that it would be a UIImage (https://www.hackingwithswift.com/example-code/media/how-to-pixellate-a-uiimage), instead I found that SKEffectNode grants access to CoreGraphic's filters, and so was able to achieve the same thing:

        let pixelateNode: SKEffectNode = SKEffectNode()

        let pixelFilter = CIFilter(name: "CIPixellate")!
        pixelFilter.setDefaults()
        pixelFilter.setValue(110.0, forKey: "inputScale")

        pixelateNode.filter = pixelFilter
        pixelateNode.shouldEnableEffects = true
        addChild(pixelateNode)

        let testSprite = SKSpriteNode(imageNamed: "testSprite")

        pixelateNode.addChild(testSprite)

The code will pixelate the sprite, but I was looking for a transition from one state to another i.e. the defaul (normal) state, to the 110 value pixelation.

Is there a way of doing this please ?

I have managed to simulate Apple's Core Image "CIPixelate" filter working with a transition.

Prepare by trawling all SKNodes on the scene and moving them to an SKEffectNode, which allows the filter to be applied to all its children in one go. Then place each iteration from a loop e.g. 1-20 (sweetspot) in a DispatchQueue with enough time for the pixelation effect to seem real.

//ITERATE OVER EACH PIXELATION REQUEST TO CREATE AN ANIMATION
for num in 1...20 {
        let seconds = 0.3 + 0.1 * Double(num)
        DispatchQueue.main.asyncAfter(deadline: .now() + seconds) {     
            effectNode.filter = CIFilter(name       : "CIPixellate",
                                         parameters : [kCIInputScaleKey: (num)])
        }
    }

Finish by calling the scene transition function after the filter has had enough time to complete (I probably should use a dependency operation) gives the desired impression.

ref : https://github.com/rHockWorks/PixelationTransition/