There is an issue with SonicWall NetExtender and Microsoft 365 authentication.
The VPN Client NetExtender modifies this key in the registry
Which causes authentication with all Microsoft 365 applications to fail.
This issue kept popping up in my environment over and over, and after deleting this key it fixed. It was only happening on client machines that had Dell SonicWall NetExtender installed. Posting this here so other professionals can see the fix.
reported the problem to sonicwall and tim