On October 13, 2020, Office 2016 for Mac and Office 2010 reach their end of support. After that date, Microsoft will no longer provide technical support, bug fixes, or security updates for either version.
Also, as previously announced, after October 13, 2020, customers will need to be using Microsoft 365 Apps for enterprise,* Office 2019, or Office 2016 in order to connect to Office 365 services. Microsoft will not take any active measures to block older versions of the Office client from connecting to Office 365 services, but these legacy clients may encounter performance and/or reliability issues over time.
Join this "Ask Microsoft Anything" (AMA), May 5, 9:00-10:00 AM PT, to submit questions about upcoming changes: https://aka.ms/OfficeEOSAMA