Please verify the client you are using.
The current Plex HTPC version is v.1.71.1.346
Download: https://www.plex.tv/media-server-downloads/?cat=plex+htpc&plat=windows#plex-app
Documentation: https://support.plex.tv/articles/categories/player-apps-platforms/plex-htpc/
Regarding support for HDR & Dolby Vision, see [HDR Metadata Passthrough] - Plex HTPC for Windows .
That is the version of Plex Web.
The server version is further down the page, in Settings → Server_Name → General.
The current public release is 1.43.1.10611.
