I might have missed this feature but for now I always rely on extra tools with random results when I want to clean up my plex environment.
I would be nice if at top level (similar to the global search) we could have a find duplicate button that would allow me as an example to find my duplicate movies from my children and parents libraries.
Thanks
Using the Plex Media Player if you go into a library and click on the “All” menu in the upper left of the library screen, you can change it to “Duplicates” and it will show you the dups in that library.

This filter shows only library items with duplicates. Then you can press the Pencil icon on the poster to show you the “Edit” screen. Then press “Info” on the left of the “Edit” screen to see the files & their locations.
How does one go about using Plex to find duplicate items across libraries?
In my example, I have media that I’ve not yet seen. I’ll later watch and determine I want to purchase.
I later purchase, encode to my format quality and liking, then forget to delete/remove the borrowed file that’s often lesser quality or less compatible format.
Interesting. Hadn’t thought of that as I haven’t run into that situation. The “To Purchase” directory is added to the “Movies” library instead of a separate one.
I have a “holding” library for raw mkv rips before I process them. Then when they are processed, I delete the entire holding area.
The more I use Plex the more I’m integrating into my main library. I recently got rid of a separate ‘Music Movies’ library and put them into the Movies library. Let’s me better use the built-in Plex tools like Duplicates or the Genres filter.
If I put the ‘To Purchase’ directory under the same movie library, that would make it difficult for friends/family to know what content I want for gift seasons, and, when I’m out shopping for myself, I hate having to dig all the way down to ‘get info’ on my mobile to determine where something is on the file system. Also, there have been times when mobile didn’t have ‘get info’ (fortunately, that’s been remedied as of late, as I find it helpful at times)
If I manually search for something and it comes up twice, I know I’ve likely forgotten to delete the original copy. I’d like to find a way to have Plex tell me what’s duplicated between libraries, but not stored in same directory.