Cloud accounts · Cloud apps on your Mac
Where do Google Drive, Dropbox and OneDrive keep their files on my Mac?
Short answer: Recent versions keep them in a CloudStorage folder inside your user Library, shown in Finder's sidebar under Locations. Storage Studio finds these folders on its own.
Recent versions of these apps use Apple's built-in system for cloud providers, so their folders live in a CloudStorage folder inside your user Library and appear in Finder's sidebar under Locations, each with the provider's name. Older setups may still keep a folder directly in your home folder. Don't move or delete that folder by hand — the cloud app may treat it as you deleting your files.
You don't need to go looking for them in Storage Studio: it finds the cloud folders that exist on your Mac by itself. They show up as Folders on this Mac when you pick a destination in Data Parking, and in Preferences → Rules → Free Up Space includes, where each provider is listed with how much space its downloaded files take on this Mac.
See how much space your cloud apps use and moving the folder to an external drive.