QSerialPortInfo uses a hard wired list of class ids to find the ports from the device driver list. So it can only find a limited set of the large set of serial port implementations available in windows. For example it will not find virtual ports of the virtual null modem of agg software (http://www.virtual-null-modem.com/).

Attached you can find the more robust function I use in my old own serial port implementation to find the ports. It should work with all existing and future serial port implementations.