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The LG 4K Ultra HD Smart TV with webOS 2.0 (2015) doesn't support HDR but you can still use it to watch 4K Blu-ray content from the Xbox One S.  

Once you connect the LG 4K Ultra HD Smart TV with webOS 2.0 (2015) to the Xbox One S using a HDMI cable, you can see from the LG TV that 4K resolution is achieved.  

Using the Xbox's '4K TV details' function, you can also verify that the LG TV supports certain 4K resolution frequencies and doesn't support HDR10.

You can watch 4K videos through multiple sources on the Xbox One S including 4K Blu-ray, Netflix, and YouTube.