Everybody with a cinemascope (1 : 2.35) projector screen knows about this problem: Plex doesn’t let you set the vertical position of subtitles. This means, subtitles are outside of the projection screen.
Infuse on Apple TV has this feature, but I prefer the UI of Plex.
An alternative would be a flag in the settings: “Always show subtitles inside the picture”, because in cinemascope movies, the subtitles are outside (below) of the picture, and that’s the whole problem.
There’s already a feature suggestion covering that exact topic.
Please use the forum search before posting duplicate requests to avoid distracting votes.