OneNote for Mac and Office 365 ProPlus subscribers = Broken
Customers with an Office 365 ProPlus only subscription (and no access to OneDrive for Business) who try to activate OneNote end up without being able to create a new notebook since the program does not support creating books offline or in SharePoint on-premise or in OneDrive for Business on-premise or iCloud or Dropbox or even just locally on the computer.
These users then get forced to register a Microsoft account to get up an running and even that is not intuitive (clicking your name and adding service)...
Soen Trueman commented
This is also true for PC users. I have two accounts - One personal and one for office 365 (business). And yet, doesn't matter which one I use, I just can't open any office 365 notebooks.