In my experience you have to sort shows into directories and sub-directories for a series.

My entire jellyfin library is just symlinks into where my crap has accumulated over the years.

https://jellyfin.org/docs/general/server/media/shows/

I have the series in their own folders. I tried to do a more nested structure to no avail. After a day of attempts to fix it I switched to Plex and it despite having its own quirks just worked fine.