Hi,

Serial Debug

The Serial debugger will work with the SerialUSB port. If you own code sends without line terminators or send byte or reads the port then you should configure the debug to use an alternative serial port or softwareSerial.

Hardware Debug

I don't think the feather has EDGB on-board? In which case if you want to use the hardware debug options you would need an external debugger. The new hardware debug options require an external debugger which Visual Micro should already support. If not then let us know.

Does this help?

I think your board has the Atmel EDBG hardware debug chip on the usb port. So in visual micro you can select hardware debug and the EDBG debugger. This should give you live step and variable watch.

If you have not invested in another device for debug then your other option is the software/serial debugger which you can find an overview of and usage guide in the documentation section accessed at the top of visualmicro.com or from within the IDE vMicro>Help menu.

If you want to use the Serial debugger on SerialUSB you might need to set the word SerialUSB into "vMicro>Debugger>RemotePort"

When using the Serial debugger on the upload/usb port, your own code might also use Serial.print or SerialUSB.print() etc. In this case use Serial.println() or SerialUSB.println() after you have output some serial. This ensures a line terminator \r\n is sent. 

If your own serial code performs a .read() on the serial you will need to follow the document of how to debug using Other Ports and Pins