Just a short post for this one but this issue had me going around in circles all day. Hopefully, this saves anybody else doing the same!
To set the scene here - I had just deployed new Azure Virtual Desktop (AVD) hosts using Azure Image Builder using the Windows 10 Multi-Session with M365 Applications image. Everything looked great until I noticed that my known-folders (Desktop, Documents etc.) hadn't redirected to OneDrive. I had set the "Silently move Windows known folders to OneDrive" policy using Group Policy so I assumed this wasn't applying but after running GPRESULT I could see it applying. I then decided to check the Back Up tab manually within the OneDrive for Business settings. To my surprise the Back Up tab was missing within the OneDrive for Business client - the other tabs were showing but not Back Up.
I had then convinced myself that it had to be a policy that was stopping the client from backing up the known-folders to OneDrive, or even modifying the configuration. I re-checked all of the group policy items for OneDrive such as "Prevent users from redirecting their Windows known folders to their PC" and "Prevent users from moving their Windows known folders to OneDrive" but none of them were set.
I spent almost a full working day checking every policy item, registry key, log file, event logs, and anything else I could think of.
This customer used Cisco Umbrella for DNS based web-protection. Upon checking the Cisco Umbrella dashboard I could see several blocked URLs:
I permitted these URLs (as per Required URLs and ports for OneDrive consumer - OneDrive | Microsoft Docs) and after restarting the OneDrive for Business client the Back Up tab appeared and the Known-Folder Move (KFM) kicked in and worked successfully.
Silly mistake to make but it was tricky to get to the bottom of as there were no errors or warnings to indicate any sort of connection issues. I could authenticate successfully and the only visible issue was the lack of a Back Up tab and the known-folders failing to move or redirect.