What has worked for me is to add the 4k version of the movie to my library. Then use the Plex Optimize process to pre-transcode a 1080p version. Then the user can select the … menu and they will see “play version” It seems some clients will surface the “pick version” menu anytime they click play but some won’t. Whenever I get a new 4k movie I optimize it until remote people have watched it and the I usually get rid of the optimized version. I also do it when I download a copy of the movie for offline playback (which believe it or not does work successfully….sometimes. But better than the never it was for a long time)