I am executing the example code of LibUsbDotNet which will return me the information of all connected usb devices. You can find this code below.
using System
The documentation says that
Gets a list of all available USB devices (WinUsb, LibUsb, Linux LibUsb v1.x).
and
Use this property to get a list of USB device that can be accessed by LibUsbDotNet.
If you are using the standard HID driver for your mouse and keyboard and haven't replaced that with the libusb.sys driver, then LibUsbDotNet can't access those devices and therefore doesn't list them.