Hi Alex,
Welcome to Microsoft Community.
I'm Hahn and I'm here to help you with your concern.
To restore an entire OneNote notebook from a backup, you can follow these steps:
- Open OneNote and create a new notebook with the same name as your original notebook.
- Close OneNote.
- Locate the backup folder that contains your notebook backup.
- Copy the entire folder to the location where you want to restore your notebook.
- Open OneNote and go to File > Open.
- Navigate to the location where you copied the backup folder and select the .one file that corresponds to your notebook.
- OneNote will open the notebook and prompt you to sync it with OneDrive. Click "Sync Now" to sync your restored notebook with OneDrive.
If your backup is in a folder format, you can simply copy the entire folder to the location where you want to restore your notebook. OneNote will recognize the folder as a notebook and allow you to open it. You can then sync the restored notebook with OneDrive to ensure that your changes are saved and backed up.
Restore notes from a backup - Microsoft Support
I hope this helps you recover your notebook. If there is anything not clear, please do not hesitate to let me know.
Your Sincerely
Hahn - MSFT | Microsoft Community Support Specialist