A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Hi,
Are you referring to OneNote app for Windows 10 or OneNote part of Office?
If you are using OneNote app, there is no Manual sync button as we have in OneNote Office suite. This default OneNote app automatically synchronize once you are logged-in with your account. Go to settings > Options and turn-on automatic sync.
The OneNote part of Office has manual sync option. Click on File> View sync status, select sync manually.
Hope this information helps, Let us know if you have any queries.
Thank you.