[rainman74]

quick update to my post 

Found the answer here

https://forum.kodi.tv/showthread.php?tid=335556

 4K video plays as 4K if the TV or monitor supports it. The playback itself has nothing to do with the Kodi surface resolution, which in most cases will be 1920x1080 (if you don't change it manually).

@fritsch Maybe you could adjust Kodi to display the actual playback resolution and not the GUI resolution. This is really confusing otherwise and I see hundreds more questions that will ask the same thing over and over again.