Mac storage basics · Finding big files, Downloads and the Trash
Do files in the Trash still take up space?
Short answer: Yes — the space is only freed when you empty the Trash. Files trashed from an external drive free space on that drive when you empty the Trash with it connected.
Yes. Moving something to the Trash only moves it; the space is freed when you empty the Trash (Finder → Empty Trash, or right-click the Trash in the Dock). External drives have their own hidden trash, so files deleted from a drive free space on that drive only when you empty the Trash with it connected.
Emptying the Trash is permanent, which is why Storage Studio never does it for you — it shows how much is sitting there and lets you open it.