OneNote won't start, won't sync, not in system tray, not working.

Navigate to the following registry key:
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\OneDrive 

Check if any of the "Disabled" keys are set to 1.  If they are, set them to 0.

https://support.microsoft.com/en-us/office/onedrive-won-t-start-0c158fa6-0cd8-4373-98c8-9179e24f10f2