BL0812's post is actually right. Setting the TV to 4K SDR and matching frame rate and content will give you the best/most accurate picture quality across all sources. Since most sources aren't native 4K HDR or Dolby Vision, setting the tv to 4K HDR/DV will try to trick the tv into displaying the source in DV which will make the picture look very dark/dull and sometimes even washed out because the source can't display the image how ATV is telling it to.
Setting the tv to 4k SDR with matching frame rate and content will allow sources that DO support HDR or DV natively to display at the best quality possible, but won't force other content to display this way if its not supported by the source.
I know it sounds backwards, but give it a try and you will see a world of difference.
BL0812's post is actually right. Setting the TV to 4K SDR and matching frame rate and content will give you the best/most accurate picture quality across all sources. Since most sources aren't native 4K HDR or Dolby Vision, setting the tv to 4K HDR/DV will try to trick the tv into displaying the source in DV which will make the picture look very dark/dull and sometimes even washed out because the source can't display the image how ATV is telling it to.
Setting the tv to 4k SDR with matching frame rate and content will allow sources that DO support HDR or DV natively to display at the best quality possible, but won't force other content to display this way if its not supported by the source.
I know it sounds backwards, but give it a try and you will see a world of difference.