It is important to be aware of the difference between backing-up and syncing your data, two very different processes that if confused often lead to data loss.
Backing-up is a process by which data is copied from one location to another for storage purposes. This stored data can then only be changed if the user opens the storage location and actively changes or deletes that data.
Syncing means that changes made to data stored in one location will be immediately reflected across all the devices or locations where that data is accessible or stored. If you change or delete your data on a device that is syncing with another device or location, that change will happen across all the devices or locations with which you are syncing.
Read how Nebo syncs your notebooks: About the sync feature