Serial.print not working, Simple "Hello world"

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[env:uno]

platform = atmelavr

board = uno

framework = arduino

monitor_port = COM8

monitor_speed = 9600

this is my platformioi.ini file

my main.cpp is
#include <Arduino.h>

void setup() {
// Initialize serial communication
Serial.begin(9600);

// Print "Hello, World!" to the serial monitor
Serial.println("Hello, World!");

}

void loop() {
// Your main loop code here
}

The serial monitor probably starts too late to catch the message.

Have you jsut tried pressing the reset button on the board after the serial monitor started up?