Why suggest diagnosing antenna issues if there’s no confirmation that the original poster can even “talk” to the device over the serial interface (e.g., by sending version or config command)?
Every time you connect a serial interface device, you first confirm that the serial2usb device is recognized (it is, in this case), then you confirm you can send commands and receive responses (not done yet!), baud rate is set correctly, etc.
And only then you try hooking the device up to some sort of complex services (rtk2go, etc.)
Logical troubleshooting is dead as a skill.