The following is supposed to create an isometric lattice pattern across a UIView, but all it does is turn the page black:

class IsometricGrid: UIView {

    let gridSpacing: CGFloat = 20

    override func draw(_ rect: CGRect) {

        let context = UIGraphicsGetCurrentContext()

        context?.setStrokeColor(UIColor.black.cgColor)
        context?.setAlpha(0.2)
        context?.setLineWidth(100)

        for x in stride(from: 0, through: self.frame.width, by: gridSpacing) {
            for y in stride(from: 0, through: self.frame.height, by: gridSpacing) {
                // Draw the diagonal lines for the isometric grid
                context?.move(to: CGPoint(x: x, y: y))
                context?.addLine(to: CGPoint(x: x + gridSpacing, y: y + gridSpacing))
                context?.strokePath()

                context?.move(to: CGPoint(x: x + gridSpacing, y: y))
                context?.addLine(to: CGPoint(x: x, y: y + gridSpacing))
                context?.strokePath()
            }
        }
    }

}

        let isometricGridView = IsometricGrid()
        isometricGridView.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height)
        view.addSubview(isometricGridView)

I am using an older version of Swift, but this is CoreGraphics and nothing new. Perhaps it is the iPhone XR emulator ?