In OneNote Online, there’s typically no need to manually save or sync your notes while you work. OneNote continually syncs your changes in the background, leaving you free to concentrate on your thoughts and ideas.
If you’re working on time-sensitive projects in shared notebooks that are simultaneously co-authored by multiple people, you may want to manually sync any large page changes that you’ve ,made so that others can see them immediately. While this is not currently possible in OneNote Online, you can use the OneNote desktop app on your Windows PC or on your Mac to manually sync notes when needed. For more information, see either of the following: