Measuring and Improving Serial Performance / Serial.flush() Blocks Forever on Nano 33 BLE Sense

Official Hardware Nano Family Nano 33 BLE Sense
2

This was fixed by replacing UART::flush() with the following:

void UART::flush() {
#if defined(SERIAL_CDC)
	if (is_usb) {
		while(!_SerialUSB.writeable());
	} else {
		while(!_serial->obj->writeable());
	}
#else
	while(!_serial->obj->writeable());
#endif
}

In the file 'cores/arduino/Serial.cpp'.