PC with O365?
Std Office repair
Restart the PC, once fully loaded, repair Office,> Apps & Features>Select Office your version>Modify /Repair, once the repair completes re-test (Quick repair)
O365 when installed under a Win user admin account, and run from that admin account, auto logs in when the PC is started. There is no separate login for any component.
OneDrive is not a backup, it’s a cloud location of your data.
The default installation of Office 365 and its OneDrive component uploads all the contents of the PC \My Documents\ folders to OneDrive, (syncs) and there will be a OneDrive folder in File Explorer containing cached copy of all the OneDrive content. And in Word etc the default Save location is set to OneDrive.
No Docs/data is stored on the local PC
You cannot remove OneDrive on a retail O365