Serial.print not working, Simple "Hello world"

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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

// 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?