I’ve followed the guide for activating opensubtitle support. Enabled the agent, user/pass OK, and refreshed the whole database.
Normally I should see an extra field “MORE” in the subtitle selection. This is not the case with me: I can see the embedded subs, and 2 subs referred to as “SRT External” (but there are no external subs added to that specific movie I picked?) So is Plex downloading this automatically ? I prefer choosing the sub myself (as in Kodi) , so I can pick the right version.
Some people use the Sub-Zero plugin. You can also manually download subtitles, name them appropriately, and add them to the folder with the movie/show. See Fetching Internet Sourced & Using Your Own Subtitle Files for additional information.