You may run into the following error when trying to perform restores from Veeam for Microsoft 365: The specified Azure AD application is missing required delegated permissions (Microsoft API: Microsoft Graph, permissions: Sites.Read.All)
This issue seems to be caused by upgrading from previous versions of Veeam for Microsoft 365, specifically version 5 to version 6.
The quick fix for this is simply to edit the organization in the Veeam for Microsoft 365 console, and run through the steps to Automatically register a new Azure AD application.