When viewing a device group entry from the Managed FortiGate table on Device Manager > Device & Groups, the device group entry is displayed in an expanded hierarchical view and the device listings within the group entry are displayed by default.
You can collapse or expand the device group entry in the table. From the toolbar above the table, you can create, edit, and delete device groups.
The maximum number of device groups that can be created is the same as the maximum number of devices/VDOMs supported for your VM license or model. See the FortiManager data sheet on https://www.fortinet.com/ for information about the maximum number of supported devices/VDOMs for your VM license or device.