@Worawan Apitanawit Update(Preview) tab within Azure update manager provides the list of pending updates that need to be installed on the virtual machines. If there are none, then the updates tab will not show any information.
This document has queries that helps you in how to get the list of pending updates or installed updates. Kindly check the queries and tweak them based on your requirement. If you face any issue when retrieving the information or couldn't find what you are looking for, kindly comment here with requirement you have with elaborate details so that I can guide you accordingly.