Serial monitor not working

I have a very simple sketch that should be writing to the serial monitor, but nothing is appearing there.

int ledPin = 13;
void setup()
  pinMode(ledPin, OUTPUT);

void loop()
  digitalWrite(ledPin, HIGH);
  digitalWrite(ledPin, LOW);
  Serial.println(42, HEX);
  Serial.println(42, DEC);
  Serial.print(F("Hello World"));

The monitor is for COM3, Arduino M0, same as the IDE (which will upload a sketch, and "Get Board Info" successfuly). The monitor BAUD rate is 9600, as specified in the sketch (and I have tried setting to something else and setting it back).

The sketch compiles and uploads, and I can tell from the timing of the flash that it uploaded successfully. Changing it to pin 1 has no effect, so not the pin interfering.

Whilst running TX does not flash (does during upload), which makes me think it is an issue with the Arduino. Sending a string does not cause RX to flash (not sure if it should, as the Arduino is not set to receive).

The IDE is version 1.8.5, the board is an M0 R3. I am connecting via USB 2.0, on Windows 10.

Can anyone tell me why it is not working?

Try SerialUSB instead of Serial.

Serial is the programming port on Zero and M0 Pro. M0 does not have it.
The native USB port is SerialUSB.

Thanks, that was it.