Apps · Offloading and restoring apps
How much space does offloading an app free?
Short answer: The app's size plus its data, because both leave your built-in drive — more than Move, which relocates only the app.
The app's size plus its data — support files, caches and the like — because both leave your built-in drive. That's why Offload frees more than Move, which only relocates the app.
If macOS protected a few items and they had to stay, those aren't counted. The Offloaded tab shows how much space each archive uses on the drive.