The request queries are as follow.
https://graph.microsoft.com/v1.0/reports/getYammerGroupsActivityDetail(date='2021-03-16')
https://graph.microsoft.com/v1.0/reports/getYammerActivityUserDetail(date='2021-03-16')
https://graph.microsoft.com/v1.0/reports/getYammerGroupsActivityDetail(period='D7')
Please check the screenshot of graph explorer below, we have tried from the admin account with all the relevant permissions, provided to the app as mentioned in the documentation.