Data Transfers · Paired devices and plan storage
What is “Included with your plan” in the New Transfer cloud picker?
Short answer: It lists storage that comes with your plan, such as Delta Drive, kept apart from accounts you connected yourself. Browse it or use its root as a source or destination like any other place.
That section lists storage that comes with your Storage Studio plan, such as Delta Drive. It's shown separately from the accounts you connected yourself because you don't need an account of your own for it.
You can use it like any other place: choose Browse to pick a folder in it, or Use … root, then Copy, Move or Sync, on demand or on a schedule.
The section appears only once storage from your plan is set up on this Mac; if you expected it and don't see it, check your plan in the License section.
Related: Delta Drive