It may not be present in Apple’s official documentation but it has been supported since Safari 12.2.
See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/da... compatibility. The demo on that page works for me in current Safari on both iOS and Mac.
Some examples seem to work better than others though. I’m on latest iOS and sometimes it will invoke the native date picker like you’d expect to see, sometimes it won’t, and the type ahead doesn’t seem to work consistently