Forum Discussion
Office 365 Groups usage report in Office 365 Admin Center
The other problem is that column only shows the last activity in terms of conversations/emails. It doesn't show the last activity from the SharePoint document library/site or Planner, etc.
As I explored in https://www.itunity.com/article/identifying-obsolete-office-365-groups-powershell-3533, determining the date of last activity in a SharePoint site is not as easy as it should be. And figuring out what happens in Planner, Teams, or anything else that uses the Groups model for identity and membership might also be much harder than asking Exchange what the last message was in a group mailbox... The interesting thing that arises from this discussion is what happens for Yammer groups where the messages are held in Yammer rather than the mailbox. I assume that Microsoft will be able to extract the date of last activity (maybe not 0001) for these groups without problems. Maybe they haven't thought about that yet...