WST can scan your library of movies and TV shows and identify them on TMDB quickly and with very high accuracy. I haven't found another tool that has better accuracy. And even if it fails to identify something, you can make corrections to override the heuristics algorithm. Then you can create a "view" of your library specifically for Jellyfin or Plex, so they are able to inherit the TMDB IDs, episode IDs, etc.

I made WST because I wasn't satisfied with Jellyfin's identification system, and the ArrStack has various issues as well, e.g. importing a library has strict structural requirements. WST does not place any requirements on how your files are organized or named, and it will never rename or modify your files in any way; it does its best to match whatever patterns already exist. I currently use WST on my own library and it has nearly identified every file perfectly.

I'd really appreciate if any of you would try it out and see how well it works on your library. You don't need to fully adopt it to try it; you can review the results in the WST web UI and then make a test view for your media server and throw it away later.