an0065 describes usage of libusb and it says that libusb supports only one interface. But there is also the usb composite example which shows how to work with multiple interfaces. I think an0065 is outdated?
do you mean below sentence in section 3.3?
3.3 Interface Descriptor
An interface in USB context is a set (collection) of endpoints that can be used to communicate with the USB host. A device can have
multiple interfaces, which is called a composite device. However, the current EFM32 USB Stack does not support multiple interfaces.
An interface can implement standardized classes (e.g. HID, mass storage device etc.), by specifying the Interface Class (assigned by
USB-IF) and defining the required endpoints. Using standardized interfaces reduces the need for custom drivers.