The relevant settings have to be enabled on the back end before you receive the option to download attendance reports. MS making it available is only step 1. Your tenant admins will need to enable and configure other items before organisers will see it as
an option. In a brief test you need to press it at the end of the meeting. If you reopen a meeting, the historic info is lost. I need to do more testing at some stage.
The ability to download attendance is also set at a per user basis, so someone has to provide a list of 'organisers' or as in our case we enabled it for everyone.
"Office 365 admins need to enable it manually. Importantly, the meeting attendance
list can only be downloaded during the meeting for now:"
I know our admin had to use powershelgl to enable within a few places in the tenant, I will try and get the details, but in addition to O365, I think they had to do something if Skype as well. I'll
try and get the detail.
EDIT: - some more info
https://docs.microsoft.com/en-us/microsoftteams/meeting-policies-in-teams#meeting-policy-settings---meeting-attendance-report
"The feature is turned off by default, and Office 365 Admins need to set a Teams meeting policy to enable it. In addition, they can navigate to the Teams
admin center > Analytics & reports > Usage reports to view additional meeting attendance data. If required, IT Admins can also assign the Report reader role for the meeting organizers so they can access the Teams admin reports themselves. We invite
you to check out the official
support page to learn more about how to turn on this feature."
Hope that helps