Our practice is to copy the projects on iCloud Drive to local as an additional backup.
On the Mac, the "QuickPlan" iCloud Drive folder is created by the macOS. QuickPlan app runs in the sandbox environment, which has NO permission to create the "QuickPlan" folder directly. If you don't find the folder on your Mac, please create a project on iCloud Drive using QuickPlan on the iOS device.
Do NOT edit the same project on multiple devices at the same time.