Dear Danny,
Hello! Welcome to the Microsoft Community.
I understand that you can use OneNote and sync it normally on other devices. But you can't do this on Mac. It won't sync with other devices. I understand your feelings and I will try my best to help you solve this problem.
First you can go to the App Store and check if there is any update available for OneNote. If so, update it. Then check if the problem still exists.
If so, try the steps here:
Check if any notebooks on your Mac can be found in the OneDrive web version. Usually OneNote will automatically sync notes to OneDrive. This can determine your sync problem.
If you can find your old OneNote notes in OneDrive, try opening the notebooks in OneNote for the web (www.onenote.com). This can help determine whether the problem is caused by the server or OneNote.
- On the OneNote for Mac toolbar, select Notebooks > Notebooks > Copy Link to Notebook.
- In your web browser, select inside the address box, and then press Command + V to paste the copied URL.
- Press Enter to load the notebook in OneNote for the web.
If you are able to successfully open the notebook in OneNote for the web and the changes appear, the issue may be caused by OneNote for Mac. Closing and reopening the notebook will usually clear and successfully reset the connection. Follow these steps:
- On the OneNote for Mac menu bar, select Notebooks > Notebooks > Close This Notebook.
- Switch back to the notebook in OneNote for the web in your web browser, and then select Open in OneNote on the ribbon.
In addition, you also need to check whether the network environment on your Mac is normal. If the problem persists after the above steps, try uninstalling the OneNote application on your Mac and then reinstalling it to see how it works.
Here is an official article for your reference, and there are some solutions to other problems in it, see if it helps you:
Fix issues when you can't sync OneNote - Microsoft Support
If you make any progress, feel free to let me know.
Best wishes
Pyke.D | Microsoft Community Support Specialist