SpartanWaycomau 

So I do see in portal.office.com under reports there is a "email usage by app" report.  That is great and all, but that only shows our migrated cloud users.  I want to see who is using basic authentication for all the on prem mailboxes, which is still 99.9 percent of our organization.  

The_Exchange_Team  Mentioned in the original post this "

Finding impacted users

The next action you really need to be thinking about is assessing client impact. The first question you probably have is – so how do I know who’s using Basic Authentication in my tenant? Great question, and soon we’ll make a new tool available to help you easily answer that question for yourself. It’s a tool that provides tenant admins with a simple way to determine who is using Basic Auth so you, the admin, can see how large of a task you have on your hands.

Once you understand what your users use, and know if they are using Basic or Modern Authentication, what can you do about it? Each of the impacted protocols have options.  "

Where is this new tool?  Need to find basic authentication on prem users.  

Get-ConnectionByClientTypeDetailReport