https://www.bleepingcomputer.com/news/microsoft/microsoft-office-update-changes-outlook-fallback-encryption/

Microsoft released the 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.

This month's KB4484511 Office update also changes the default fallback encryption for Microsoft Outlook 2016 from 3DES to AES256.