Compile and upload to Arduino Opta is succesfull, but code doesn't run

[soosp]

This simple code has been compiled and uploaded from PlatformIO 6.1.14 (VSCode 1.87.2 on Windows 11) to an Arduino OPTA RS-485, but it doesn't run. It prints nothing and the LED is dark.

#include <Arduino.h>

#ifndef MONITOR_SPEED
  #define MONITOR_SPEED 9600
#endif

#include <Arduino.h>

#define LED LED_BUILTIN

void setup() {
    pinMode(LED, OUTPUT);
    Serial.begin(MONITOR_SPEED);
    while(!Serial);
    Serial.println("Starting...");
}

void loop() {
    digitalWrite(LED, LOW);
    delay(1000);
    Serial.println("Low");
    delay(1000);
    digitalWrite(LED, HIGH);
    Serial.println("High");
    delay(1000);
}

platformio.ini is here:

[env:opta]
platform = ststm32
board = opta
framework = arduino
monitor_speed = 115200
build_flags =
    -DMONITOR_SPEED=${this.monitor_speed}

If you try to compile and upload it from Arduino IDE 2.3.2, it works well (prints to the serial console and LED is blinks).

I have had similar experiences with other sketches.