I have not found much on this. one old post almost 2 years back with no feedback. I know I’m in the minority of user with dedicated space, let alone not running 16x9 screen.
I have a dedicated theater space in my house and I have a 120" widescreen scope screen with a projector. it is 2.40:1
The UI on the Plex app (using 2017 Shield for client) is 1.85:1
I am not using any anamorphic lenses, Just lens memory on the PJ itself. When I watch a 2.40:1 movie (most movies) I press a button and the pj zooms in and the picture fills the screen while projecting the black bars above and below the screen.
How about an aspect ratio option in the UI?? (not a resolution setting)
This can be done in Kodi via the ScopeNox theme but I vastly prefer the Plex ecosystem.