A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
The AppData Folder is a hidden one. You could make it visible by changing the settings in Explorer. But there is a more simple way to clear the OneNote cache:
Start OneNote with the parameter /safeboot. you can do that using WIN+R, then type OneNote /safeboot and hit return. A dialog come up showing you some options. Use the clear cache option and restart OneNote the normal way after that. Hope that will help.
Usually the cache of any notebook you actually close in OneNote is flushed. So closing all notebooks *should* have the same effect. But I recommend the method above.
But first: I have to repeat what Haukeberg said: all "unsaved" (meaning: not synced to OneDrive) notes are lost in that process. So make sure first all your opened notebooks have finished syncing.