You might want to try it disabled. I experienced increased buffering of 4k movies after one of the XPlay updates a while back (and the official Plex app always had buffering issues for me). After I disabled secure connections, I haven’t encountered a single buffering instance using either app. Others have reported this setting may help with other playback issues (spinning red circle) and even pin loop problems.
Also, as to the issue with the official Plex app force-transcoding your 4k movies, I’m going to guess these are movies with TrueHD audio format and subtitles? See this thread: LG-WebOS Bug Report: 4k HDR movies with TrueHD audio and external subtitles (.srt) forcing transcoding. @bublikoff apparently found a workaround to make TrueHD work on these LG TVs without transcoding (you can see this in the Plex dashboard), which is why XPlay can play these movies without transcoding while the Plex app cannot.
