iCloud Drive makes it possible to store your projects in the cloud. Any projects you add to iCloud Drive will be synced across your devices. If you choose to permanently delete a drawing or folder from iCloud Drive, then it will be gone from all of your devices for good.

iCloud backup means that your whole device is backed up to iCloud at certain times, depending on the device settings. iCloud backup does not allow you to recover a single app and its content, nor does it allow you to sync individual projects across devices.