Starting April 13th, direct reports Office 365 Groups will be automatically created for managers.

If managers do not have permission or if you have turned off the ability to create Office 365 Groups, these direct reports groups will not be created.

If you want to disable this auto provisioning, you need to turn off the directreportsgroupautocreationenabled by connecting to Exchange Online using Powershell and run this command

Set-organizationconfig -DirectReportsGroupAutoCreationEnabled $false