How to get Android's screen width and height

Inside your Activity:

override fun onStart() {
    val size = Point()
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.R) {
        requireContext().display!!.getRealSize(size)
    } else {
        val windowManager = requireContext().getSystemService(Context.WINDOW_SERVICE) as WindowManager
        windowManager.defaultDisplay.getRealSize(size)
    }
    size.x // Width
    size.y // Height
}