OneDrive Backup and OneDrive Sync are different in the following ways:
OneDrive Backup creates a separate copy of your files to protect them in case of disaster, while OneDrive Sync keeps your files updated across multiple devices.
OneDrive Backup is a one-way process from your device to the cloud, while OneDrive Sync is a two-way process.
OneDrive Sync is useful for editing files on multiple devices and accessing the latest version of files. OneDrive Backup is used to keep your data secure.
OneDrive Sync is not intended for transferring large amounts of data, and files that are not stored in synchronized folders are not synchronized