User Configuration > Administrative Templates > Microsoft OneNote 2016 > OneNote Options > Password
User
HKCU\software\policies\microsoft\office\16.0\onenote\security
OneNote supports password protecting sections and they are unlocked once a user types the password and can be locked again by either a timeout period or when you navigate away from the section. This option will lock the section after the user hasn't used the section for the selected amount of time.