Rarely, a connected app stores data in a “hidden” location within your Google Drive. You can check for these apps by visiting https://drive.google.com/drive/u/0/settings . If you see anything that looks like it might be holding data you can use the dropdown “OPTIONS” menu on the right to “Delete hidden app data”. Make sure you don’t need the data before choosing this option. After doing so, you should see your storage decrease within a few hours.
