All,
Ive tested OneNote for Mac (native app version. MacOS Mojave)and Onenote for windows OneNote (windows 10 professional) Version 1803. Sync does work in real time, However, it is a bug in that no confirmation of sync completion is done. (also, verified it works
with Sync on Onenote for Web(via web page access).
For example, I wrote a test sentence in OneNote for Mac and it properly shows up and syncs all notebooks and changes to my Onenote on my Windows Device. Hope this helps troubling shooting of the issue,
(it is not sync issue, rather no confirmation or webserver response properly saying sync was done accordingly)
Update: Just prior to posting this. found the issue to resolved.