If you enable this options, your main.cpp should be formated like any other sketch

//file: main.cpp
#include <M5Stack.h>

void setup(){

  M5.begin();
  M5.Lcd.printf("hello world");
}

void loop() {

  M5.update();
}

Else you need to implement app_main() and call initArduino(); in it.

Keep in mind that setup() and loop() will not be called in this case. If you plan to base your code on examples provided in esp-idf, please make sure move the app_main() function in main.cpp from the files in the example.

//file: main.cpp
#include <M5Stack.h>

extern "C" void app_main()
{
    initArduino();
    M5.begin();
    M5.Lcd.println("hello world!");
}