The Plex company has released two updates for its tvOS app following the launch of Apple TV 4K. The first update (version 1.18) was pushed out in late October and the second update (version 1.19) was pushed out this week.
The first update features support for 4K video playback on Apple TV 4K. In addition, it adds support for “direct playback of FLAC music” on tvOS 11, meaning both versions of the Apple TV box. The second update adds support for “direct play support for HEVC video codec” on tvOS 11 (both Apple TVs). That is possible because Apple has enabled native support for the formats with the release of tvOS 11.
Plex on Apple TV 4K does not yet offer support for HDR video.