JS - touchstart / end events not working on iOS

I'm trying to fire a function through a swipe gesture using the touchstart / touchend events. It works perfectly on Android (tested on Chrome and Firefox) but not on iOS (tested on Safari and Chrome).

The page I'm working on : https://www.collectifbam.fr/design-critique/

The script :

  let touchstartX = 0;
  let touchstartY = 0;
  let touchendX = 0;
  let touchendY = 0;

  const gestureZone = document.querySelector('.presentation');

  gestureZone.addEventListener('touchstart', function(event) {
      touchstartX = event.changedTouches[0].screenX;
      touchstartY = event.changedTouches[0].screenY;
  }, false);

  gestureZone.addEventListener('touchend', function(event) {
      touchendX = event.changedTouches[0].screenX;
      touchendY = event.changedTouches[0].screenY;
      handleGesture();
  }, false);

  function handleGesture() {
      if (touchendX <= touchstartX) {
          nextSlide()
      }

      if (touchendX >= touchstartX) {
          prevSlide()
      }
}