I think you need to do more research. I just played Battlefront II on my S over the weekend in full 4k HDR. I can confirm this because on my TV, I can navigate to it's display information in the settings menu and it will tell me at what resolution the current content is and whether or not it's HDR. While it may not be NATIVE 4k, it is still up-scaled and displayed nonetheless.
The Xbox One X can native handle the 4K H.265 from media server or USB drive while the Xbox One S only allows you to stream H.265 files with the online streaming services.