In Emby there is a plugin called "Genre Cleaner" that takes diverse genera tags and maps them, as the user chooses, to a smaller, more sensible, set.
As example it can take "Romance" and "animation" and "Family" and map them all to "Drama". BTW: I use "Drama" as a catchall for genera that I do not want to have separate. It also can map "Science Fiction" to "Sci-Fi" so that there is only one category for science fiction movies.
My question is: Does Plex have a similar plugin that hopefully is easy to use and simple to set up?