Last I checked (which admittedly was a few years ago), Plex was the only thing that could add subtitles to something being Chromecast’ed. That’s the primary way I watch things on my actual TV, and since apparently I’m deaf AF and need subtitles for everything, Plex was the best choice. The others would’ve required processing stuff with handbrake ahead of time.
Bought a lifetime subscription though and it’s been well worth it.
There’s apparently a plug-in for Jellyfin to do the subtitles download thing… haven’t tried it though