This has been how Plex treats specials for ages – it’s not specific to media you find in Discover.
There’s an existing feature suggestion asking for an option to not include that particular season in the total season count of a show.
While interest in this suggestion has been rather low, I suggest you comment/vote in that thread in order to avoid further distracting/cannibalizing votes. Unless I’m missing some specific aspect, I’ll close this thread as a duplicate.
