If you are using the Apple TV app, there is a bug that keeps it from flushing its cache. This is probably due to serve bandwidth issues so that users who pause or rewatch content don’t consume GBs of data for the same show or movie.
Deleting the TV app will free up a ton of space, if you stream a lot of content.
The same bug effects Facebook, Instagram, YouTube, Google Drive, etc. So try deleting and reinstalling those kinds of apps as well.