One issue I currently have with the regular Plex app is that HDR playback on an iPad 10th gen is washed out when direct playing. I know the iPad doesn’t really support HDR, but an iPad mini (6th gen) plays HDR content without being washed out.
However, with the preview app now, HDR playback is no longer washed out on the 10th gen iPad - not sure what changes were made to the player but good to see!