User Configuration > Administrative Templates > Microsoft OneNote 2016 > OneNote Options > Other
User
HKCU\software\policies\microsoft\office\16.0\onenote\options\other
This policy setting controls whether Purview Sensitivity Label capabilities can be enabled for OneNote Sections. If you enable this policy, users can use supported Purview features, such as manual labeling, label removal, or default labels, to apply sensitivity labels to OneNote sections and help protect sensitive information. At this time, mandatory labels, auto labeling, and dynamic watermarking are not supported. If you disable this policy, users won't be able to apply, change or remove Sensitivity Labels in OneNote Sections. If you do not configure this policy setting, users won't be able to apply, change or remove Sensitivity Labels in OneNote Sections.