You should avoid transcoding 4K especially HDR as the HDR will be transcode by the CPU and not GPU. If you do not have the horsepower to Transcode 4K HDR then I would recommend making optimized versions 1080P of the movie so Plex can use that for your non 4K TVs and remote users.
You might find this thread useful: [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k
