Since I had difficulty finding simple information on how to connect the RAK in serial I write the explanation here:
To configure RAK you don’t need a USB to serial adapter. Just a simple USB cable!
Once the USB cable is connected to the computer, check if your RAK needs the battery connected or not (on the product page).
Connect the cable to the RAK, install the serial drivers and don’t forget to download RAK_SERIAL_PORT_TOOL from here:
https://downloads.rakwireless.com/en/LoRa/WisTrio-LoRa-RAK5205/Tools/
at this point you can configure your RAK following the guide and using the software you have installed!