If there were a subtitle burn in option in the Plex Optimization module then one could move away from having to use handbrake all together… The Optimization routine is really convenient and a great asset to Plex if it didn’t auto delete the optimized versions when the original was deleted or moved, and you could select to burn in sub titles…
Subtitles are already burned in, if they were ‘selected’ prior to the Optimization.
This applies to the ‘Mobile’ optimization profile always.
If you use the ‘TV’ profile, only bitmap-based subtitles are burned in, text-based subtitles are added as side-car subtitle files by the optimizer.