Mac storage basics · Finding big files, Downloads and the Trash
Why is the Movies folder in my home folder so big?
Short answer: Video apps keep their libraries there — iMovie, Final Cut Pro, the TV app's media — plus saved recordings and exports. Find the biggest item and manage it in its own app.
Video apps keep their libraries there by default: the iMovie library, Final Cut Pro libraries, the TV app's media folder, and often screen recordings or exports you've saved there. Any one of them can be tens of gigabytes.
Open the folder in list view with sizes turned on to see which item is biggest, then deal with it in its own app — don't delete parts of a library by hand. Specifics: the iMovie library, Final Cut libraries, TV downloads.