The System Requirements section of the Veeam Backup for Microsoft Office 365 User Guide.
Note
Consider the following:
To restore SharePoint content database items from a server running Microsoft Windows ReFS, the Veeam backup server or a management console must be installed on the Microsoft Windows Server 2012 or later.
To restore from a server running Microsoft Windows ReFS 3.x, Veeam backup server or a management console must be installed on the Microsoft Windows Server 2016.