folder metadata organisation

[TheDreadPirate]

Correct. Your options are your media directories or Jellyfin's app directory and database.

This is currently not configurable beyond that and I am not aware of any efforts to make it configurable.

HOWEVER, if for disk space reasons you do need metadata located on a different location from Jellyfin and/or your media, you could use symlinks. And with Docker you can mount specific container directories at an arbitrary directory on the host.

Keep in mind that storing metadata in this way is not "portable" like it would be if you stored your metadata/images/trickplays alongside your media. If THIS is your intent, having "portable" metadata, don't bother with the symlink suggestion. Since Jellyfin uses a UUID string for storing the metadata and that UUID will likely not be the same if you did a full reinstall of Jellyfin and didn't do any kind of restoration of the database.