I'm on Plex but ran into the same issue years ago. My method was to split Movies and TV libraries into "Movies," "Animated Movies," "TV," and "Animated TV" (also 4K TV and 4K Movies but this is all duplicate content that I don't allow to be remotely streamed).

From there, I made sure to put everything i could into collections. More recently, I've made a bunch of new movie collections based on genre, decade, director (maybe the top 15 with the most content in my library), and actor (again only the top few) and then adjusted the sort title of these collections to keep them at the top of the library in an organized fashion. ThePosterDB was great for this as I found matched poster sets for each of the above categories and so it made everything look great too.

Basically my strategy is to condense everything possible while creating new categories to easily filter things down when searching for something to watch (e.g. Action movies or 1990s movies). Some other tips are setting library filters to "unwatched" an/or creating "watch lists" of things I want to see at some point but don't feel like watching at the moment. This last one is a Plex feature but you could use something else like IMDB or Trakt to do the same.

It can definitely be a chore to find something to watch when you have several thousand choices between TV and Movies so anything you can do to knock those numbers down will help. Something else you might look into is setting up PseudoTV, ErsatzTV or something similar. These allow you to create your own "TV channels" using your content meaning you'll have channels "playing" predetermined content constantly giving you something to flip through when you can't decide on something specific. It even gives you the option to insert old commercials or change content based on the time of day so you can really mimic old network TV.