Hi @alein
Do you set access permissions for users in SharePoint? If a user is granted access to a notebook in a private channel through SharePoint, removing the user from the team or private channel won't remove the user's access to the notebook.
Also, if an existing notebook is added as a tab to a private channel, access to the private channel isn't changed and the notebook retains its existing permissions. For more details, see: Considerations around file access in private channels.
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