Currently, Android users are able to play YouTube videos at a maximum resolution of 1440p, but Google has added support for 4K HDR support for the YouTube App. This enables the Android users to stream videos in 4K along with HDR enabled. Earlier 4K video support is for only iPhone users but now Android users can also enjoy the moment.
If any YouTube video is uploaded in 2160p (4K), earlier Android's YouTube App show only 1444P max resolution, but from now they can go up to 2160P on their YouTube App. To change the resolution, open a video and touch the three-dot menu on the top right corner. If your device has a 2K or 4K screen you can increase the resolution.
Streaming videos at 4K requires a stable connection of 20Mbps and also consumes more Data and Battery, hence you will encounter some great dip in the battery while streaming videos. To get 4K HDR support you just need to update your app from Google Play Store.
Apart from Android users, HDR support has been added to the XBOX console. The feature is available on the new generation Xbox One S and Xbox One X along with the latest-generation Xbox Series S and Xbox Series X consoles, according to YouTube support.
The maximum resolution you can have a playback is highly dependant on the screen that you are using.