Policy
Embedded Files Blocked Extensions
To disable the ability of the users in your organization from being able to open a file attachment of a specific file type from a Microsoft OneNote page, add the extensions you want to disable using this format: ".ext1;.ext2;" If you want to disable the opening of any attachment from a OneNote page, see the Disable embedded files policy. You cannot block embedded audio and video recordings (WMA & WMV) with this policy instead refer to the Disable embedded files policy.
5961b18990a7 L_EmbeddedFilesBlockedExtensions Registry
Copy registry mappings
HKCU\software\policies\microsoft\office\16.0\onenote\options\embeddedfileopenoptions\blockedextensionsPolicy notes
To disable the ability of the users in your organization from being able to open a file attachment of a specific file type from a Microsoft OneNote page, add the extensions you want to disable using this format: ".ext1;.ext2;" If you want to disable the opening of any attachment from a OneNote page, see the Disable embedded files policy. You cannot block embedded audio and video recordings (WMA & WMV) with this policy instead refer to the Disable embedded files policy.