Microsoft released September 2020 non-security Microsoft Office updates with performance improvements and fixes for several issues affecting Windows Installer (MSI) editions of Office 2016 and Office 2013 products. The September 2020 updates can be manually installed from the Download Center or by using the Microsoft Update service for automatic installation. The updates apply to Microsoft Installer (.msi)-based Office products only and do not apply to Office 2016 Click-to-Run or Office subscription editions such as Microsoft Office 365 Home and Office 365.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-office-update-changes-outlook-fallback-encryption/