USBPap does not support capturing on Com ports. Nor does npcap or WinPcap.
USBPCap does support capturing on USB interfaces, you'll have to determine which of the interfaces listed corresponds to your USB to serial converter.
Once you figure that out and capture the traffic, then it's likely that it still won't dissect the application traffic as most dissectors don't support USB as a transport media.
To capture such serial traffic and dissect it I use an Ethernet to Serial "Terminal Server", e.g. a Lantronix device as shown here which provides a virtual serial port for the application but transits the data over TCP to the terminal server which is then connected to the serial device. Wireshark is then used to capture the TCP traffic which does usually allow dissection.
What protocols are you hoping to dissect?