Verify that the account used to enable sync is the same account that you have signed in into OneNote. Is OneNote app installed on your phone? If you are checking on your laptop/PC, it available in Outlook in OneNote feed.
https://www.samsung.com/us/support/answer/ANS00088543/
In Samsung Notes, go to Settings and click on Sync to Microsoft OneNote > Folders to sync. Check if the folders are selected. Next, go back and click on Sync now.
