Simple answer: No. If the screen is rated to run at a refresh rate of 60Hz, that means all supported resolutions. Can a 4K monitor do 144Hz? The LG UltraGear

As long as it is 55″ or above it does support 1440p 120Hz and VRR. The 49″ is only 60 Hz though. Is 1440p as good as 4k? 1440p 240Hz

In the Plex Web Player, go to Settings > Plex Web > Quality. Selecting “Maximum” will guarantee that the client takes the best version from the video source (which should