Movies folder not showing up, not sure if permission issue

[EliteAlien]

Hi EliteAlien and geebx! Sorry for the late reply, I was busy with home stuff and put this aside for a bit.

...Docker related due to not giving Docker access to the proper media folder.
- Can you list out the actual commands for the chmod and chown.
My suggestions: sudo chown jellyfin:jellyfin -R /media/media-folder and then put other user accounts in the jellyfin group. Which gains you access to those folders from the other users. However, all the files will be recursively changed and owned by the Jellyfin user account.
- When you go in a terminal and "ls -l /media/media-folder" what is the full output.
Example of what my mounted location for movies looks like: https://imgur.com/a/yDCgqjR
- If Jellyfin in hosted in the CasaOS with a Docker container, what docker container did you use and can we see the yaml and/or how you setup the command.

Going backwards through EliteAlien's queries:
- My yaml file is here: https://text.is/0855. Please ignore the lack of indentations, this is just how the text pasted on the site. Indentations are correct in the file, I've checked.
- Example of my Movies folder is here: https://imgur.com/eW5hrFS, it's just that my user name and the group name (which both start with m) are blacked out.
- I can't define the user and group as "jellyfin" as that would block Plex, Sonarr, Radarr and Bazarr from accessing the same drives. I also wouldn't be able to access it outside of CasaOS or through a SMB share. Or maybe you have a solution for that?
- Using your suggestion, I have tried, once again, to chown this folder: "sudo chown myuser:myuser -R /media/myuser". The result was a lot of "Operation not allowed" (sorry, my system is in Brazilian Portuguese: "Operação não permitida", but I think this is the right translation into English) on a drive that mounts automatically to my system. Whenever I restart my system, I always have to open Dolphin, select the HDs for Movies and TV Shows, and type in my user's password, because they don't mount automatically. I tried changing this in fstab, but also lost access to these drives when I did it, so I changed it back. It also showed, again, folders that I have already deleted from my system and that do not show up in Dolphin. Here's a screenshot: https://imgur.com/G4rv3pz. Rebooted and... NOPE! It just refuses to access it!
- New information: now Plex also can't access the same folder. This is unrelated to the chown command above, since it began before I even checked your reply.

- That link says the Docker image in that yaml via text.is/0855 is for linuxsever/plex not Jellyfin. The docker containers yaml should look more like what Geebx listed and the volumes should be similar to how you would have setup the Plex one as well. Though with "Jellyfin".

- Yes as I mentioned in my previous post. You would need to assign all the users to that group. You don't exactly have to make the group Jellyfin, but you do need to link the users to have access to that group. You could add it to an existing group or create a new group and add all the users to that said group. 
1) sudo groupadd name-of-group (Create a new group) or sudo usermod -a -G name-of-group username (Add user to an existing group) Either create a new group and use the second command or add Jellyfin to have access to the same group Plex, Sonnar, Radarr, Bazarr, et cetera have access too.
2) If you want to make sure that a user is in a group or check the existing groups a user is in. "groups username" (This will list all groups the user is in)

- Is this like a USB drive, or is this like a Samba share mount that you tried mounting using your fstab? Also, what format is this file system in (for example, NTFS, EXT3, EXT4, BRTFS, or XFS)? Could you supply your fstab? Because if you mounted this via fstab and can't gain access this sounds like either a mounting issue or again another permission issue to where you're mounting the drive. 

- I would say it's again a group issue for Plex even. I've only used Plex for a short test and jumped off it years ago. Not via a Docker container, but a direct install and it too had to have the media in a group "Plex" to access it. Most likely this is similar, so if you ran "groups plex" you would get a list of the groups it's in and gain access to that said group. Even Emby have similar groups as well. The problem you have with this is you have to give them all access to the same group to access the files if you wish to use them all. However, you run into another issue doing this mixed platforms as well. Ownership of files can sometimes get a little messy unless force any media to change permissions on those files as standard operations can lead to copying the permissions of the files and not overriding the ownership. That is where chmod, chown, and even setfacl for the owner and groups come in. If you have separate metadata locations for each specific media server, then this should be less of an issue. My concern would be with writing the metadata in the media folders might get a little weird without setting that up as well. Once you had everything setup right you would do like a sudo chmod g+s /media-folder or sudo setfacl -Rdm g:groupname:rwx /media-folder

So you understand ACL and what it's doing.
https://www.computerhope.com/unix/usetfacl.htm