Extra local content not showing up

Server Version#: 1.22.0.4163
Player Version#: 4.53.0

I’ve not been able to get this featurette to show up in Plex at all. I’ve tried placing the file in the same dir as the main film with the -featurette naming convention, with the subfolder naming convention, with the extras subfolder, without the extras subfolder. Nothing works. All my other extras for other films show up fine. This ONE file is the only one I am having problems with. Please help.

You have one folder level too much.
Omit the Tenet (2020) - Extras folder.

You need to follow Plex naming requirements.

Plex Docs → Your MediaMovie Files (Naming and Organizing)Local Files for Trailers & Extras

Example:

/Movies
../Tenet (2020)
..../Tenet (2020).mkv
..../Looking at the World in a New Way The Making of Tenet-featurette.mkv

Also, If you use the Featurettes subfolder you do not need to add -featureette to the file name.

Nope. I did ALL of that. None of it worked.
See my OP:
“I’ve tried placing the file in the same dir as the main film with the -featurette naming convention, with the subfolder naming conventions, with the extras subfolder, without the extras subfolder.”

For the record ALL of my other files are:
/Movie
/Movie - Extras
/Featurettes
/Deleted Scenes
etc… And they all work fine.

All three screenshots above are examples of things that DON’T work, even though they should.

/Movie - Extras is not supported.
Re-scan the library if you rename/relocate files.

This works on my system:

/Movies
../Tenet (2020) [2160]
....Tenet (2020) [2160].mkv
....The Making of Tenet-featurette.mkv
..../Trailers
......Theatrical Trailer.mkv

Using a JellyFish test file in lieu of actual extras:
Screenshot (532)

So what does not work?

Literally this one file doesn’t work, no matter what naming convention I use, and I can’t figure out why.

I rescan my library after every change. Plex sees the file, it shows up for a second, and then disappears.

Please show all current contents of the Tenet (2020) folder.
Please use “list” mode.

Please excuse my ignorance, I’m not sure what you mean by “list” mode

But here are the current contents of the folder:
/Movies:
. . . /Tenet (2020) 2160p:
. . . . . . Tenet (2020) 2160p.mkv
. . . . . . /Featurettes:
. . . . . . . . . Looking At The World In A New Way The Making of Tenet.mkv

I tried that exact naming convention and filing. It did not work. For some reason Plex just doesn’t want to recognize this ONE file.

Is there really a colon : at the end of the folder name? If so, lose it.

No there is not actually colon in the folder name, as it is a character that is literally impossible to use in a folder name. Windows will not allow it.

So yeah, sorry I’m not actually sure why I put the colon in

/Movies
. . . /Tenet (2020) 2160p
. . . . . . Tenet (2020) 2160p.mkv
. . . . . . /Featurettes
. . . . . . . . . Looking At The World In A New Way The Making of Tenet.mkv

I also tried
/Movies
. . . /Tenet (2020) 2160p
. . . . . . Tenet (2020) 2160p.mkv
. . . . . . The Making of Tenet-featurette.mkv

Do you have another version of Tenet in the same library?

Nope. Just the one.

Last resort: perform the Plex Dance with the whole “Tenet” folder.