You can back up Office 365 sites from the subclient level.
Backing up Office 365 sites is similar to backing up SharePoint documents. For versioned items, you can also back up either the latest version or all versions.
For instructions to perform a backup operation, see Back Up Documents for the SharePoint Server Agent.
Notes
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While running an Office 365 backup operation to back up a parent site, you will be able to back up all the child sites in the hierarchy by default in a nested subsite. If you do not want to back up child sites in the hierarchy, create the additional setting bParentChildSubsites, and set its value as 0.
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You cannot have a library as subclient content. You can have a web application or sites or site collections as subclient content.
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You cannot browse and restore the deleted items.