With Mac OS version of OneNote, the Word and Excel attachments inserted in notes are read-only, but they can be modified on both the phone end and the pad, why?
OneNote for MAC runs in a separate sandbox. Unable to communicate directly with external programs.
OneNote's traditional attachments can be opened with local App, but they are impossible edit and save back to OneNote.
In order to be able to use editable attachments.
You can save attachments as new OneNote cloud attachments.
Then use Gem Menu for Mac OneNote add-in to open the cloud attachment for editing.
This solves the annoying problem that the OneNote for MAC attachments have not been editable all along.
MAC: How to Enable/Disable Cloud File Attachment in OneNote (Apple Version)?