Sync option enable users to keep copies in sync between SharePoint libraries and User's local disk.
Lets get started :)
We have to disable the sync option which can see on site collection level or at document libraries.
Steps to disable sync option:
1. Go to Site Settings.
2. Click on "Search and offline availability" under Search
3. Select no for offline Client Availability and click OK
4. The Sync option has been disabled.
Happy SharePointing :)