YouTube app can now play 4K HDR videos on Android devices
The quality of the image YouTube offers on various platforms is strongly related to how good your internet connection is, but that mostly matters when you're watching videos on the go. As long as you have a smartphone that supports 4K resolution, you could watch YouTube videos in high-resolution, but only if your internet connection could sustain it.
Starting this week, YouTube added the same 4K resolution option to Android devices that don't actually support it. If your smartphone has a Full HD or HD resolution display, you could theoretically watch 4K videos on YouTube.
Google has yet confirmed the new changes, but there's a whole thread on Reddit where people discuss the benefits of having such a high-fidelity option to watch YouTube videos.