If Mac OneNote prompts What's New, this indicates that the update has been received.

What's New

Local Backups

You now have the option to backup your notes on your computer as well as in the cloud. Find it in the preferences pane!

On the main menu of Mac OneNote, tap OneNote Menu -> Preferences -> Backup.

Backups Options

• Open Backup Folder
• Automatically back up my notebooks every week. We'll keep the two recent versions of each of your notebooks.
• Back Up Changed Notes Now
• Back Up All Notebooks Now