Missing Plex 4K option on PHILIPS 4K Ultra HD TV 49PUS7909

Hi
If I open plex an my PHILIPS 4K Ultra HD TV 49PUS7909 the app doesn´t show an option for 4K. 1080p seems to be the maximum limit. If I try to play 4k contant on the TV Plex will transcode it in 1080p. Why it doesn´t work? On my WinPC PlexServer and player it works without any problems.