Sorry in adavance if this has been asked before. So DL a tv series but cannot watch it through plex.
Plex can be very picky with tv shows… if the file name / folder structure doesn’t follow a certain naming convention, Plex will not even load them into your library.
you can change the names manually according to the Plex media preparation support pages or use a 3rd party app (e.g. filebot) to do the renaming for you.
another root cause could be that the file format isn’t recognized by Plex. Plex only recognizes individual media files but no DVD/Blu-Ray images (e.g. *.iso or ts-folders).
do you mind sharing some details on the files you’re aiming to add to Plex?