Microsoft is switching the default access type for Office 365 Groups to be private. It’s a change that you can easily reverse, if you want it groups to be public. The change will be effective for Outlook endpoints first, meaning OWA, Outlook desktops, and the Outlook mobile apps. Later, the other Office 365 apps that create Office 365 Groups might fall into line. Or not, as the case might be.
https://www.petri.com/office-365-groups-private-default
