The reason the COM port did not show up in Ports in Device Manager was because I made a mistake when I connected the USB. (I did not hold down the Boot button).
I flashed the Firmware (ESP32-C3_RFTest_108_2b9b157_20211014.bin) again using EspRFTestTool_v2.8_Manual.exe, but the situation remains the same.
When I plug it into another PC, the message “Unknown USB Device (Device Descriptor Request Failed)” is displayed.