Sub-Zero.bundle VS Audnexus.bundle

Sub-Zero has not been maintained since 2021 so I wouldn't consider that a good source.

For a more standalone way, look into Sub-Zero which was THE Subtitle plugin for plex.

Sub-Zero is a third party agent you add to your server

I did find a post, 3 years ago, in the Emby forum that this person did manage to have Subtitles in plex and they were in their own folder by using Subzero. However, the Subzero Plugin states:

It should, but you need to use Kitana to actually interface with it.

See here why it can work with the Plex Movie (Legacy) and why it doesn't work with the new Plex Movie agent: https://github.com/pannal/Sub-Zero.bundle/issues/753

I've used Sub-Zero plugin (https://github.com/pannal/Sub-Zero.bundle), it's quick and always has subs for the languages I need (english and spanish)

Sub-Zero

https://github.com/djdembeck/Audnexus.bundle gets you meta-data updating.

Also I noticed Audiobook.bundle is no longer being actively worked on and has been moved to a different project, Audnexus. If you want to try it, I would use Audnexus because it has a release in March.

If you don't know about Plex, it's a service where you set up your own media server. It's not designed with Audiobooks in mind but I created a Music Library and only put Audiobooks in it. Plex is great and for regular media it will scan all your files and organize it and all the the details, summaries, catalogue and everything as if it were a regular streaming services; but since it's not designed for audiobooks you need to add an audiobook source for it to pull details from. I added Audnexus as my source, it works great.

Third-party metadata agents/scanners still work (e.g. Audnexus is a popular one for getting better audiobook metadata), but there are very few others that do. Ones that relied on their own UI (e.g. anything that integrated with services like Spotify, YouTube, etc) don't work anymore, and haven't for 4+ years. You'll see their entry in the Plugins menu in your server settings, but you can't do anything beyond that because the UI it relied on was removed.

Yes, it's fairly common. In lieu of "official" support, the third-party agent Audnexus can help with organizing things, pulling from online databases that the regular Plex Music agent doesn't (e.g. Audible), and setting tags that can help with navigation (e.g. setting the Style to the narrator, so you can filter to specific narrators).