App Store 2.20.1 Release Date: December 17, 2020
Introducing "App Control Center" for Admins
Admins will now be able to set and change defaults from App Control Center, which is on the Apps & Integrations page for co-editing applications.
This will enable one-click access to the default editing application for your users to streamline the user experience. If you have other editing applications enabled and added in your domain but are not set as a default, users will still access it from the context menu (open with) as usual.
Default Editing Application: Microsoft Office Online.
Default Option for Co-Editing Apps from App Control Center
It will even make it easier for admins in one central place, instead of navigating to individual application tile to manage your settings. Clicking on "Settings" will enable you to choose or change your defaults as well as other settings.
Default Setting Option from Individual App Tile
Default Setting Option from Individual App Details Page
Client Experiences (from Web UI and from Desktop (Windows only) for Editing with Default Apps is here
Client Experience for co-editing when at least 1 person has document enabled is here and here.
Microsoft Office Co-editing solution with Desktop here and here