I am new to M5Stack but already programmed some stuff for esp8266 using platformio.

I loaded all the necessary libs and board definitions and tried a short script:

#include <M5Core2.h>

void setup(){

  // Initialize the M5Stack object
  M5.begin();

  // LCD display
  M5.Lcd.print("Hello world!");
  
}

// the loop routine runs over and over again forever
void loop() {
    M5.update();
}

Everything worked as expected.
But then I added some Code like this:

M5.Lcd.fillRect(10, 10, 100, 100, TFT_YELLOW);

or this:

M5.Lcd.fillScreen(TFT_RED);

and suddenly the screen stay black. You can only see the backlight working. When I remove the fill... rod draw.... part, it works again. What am I doing wrong?

Thanks,
Roland