@pépémax
I will give PlatformIO a go. Might give me more direction of where the issue is. Trying via VScode, supposed to be easier for casual programer like myself

In response to what you said, the M5Stack at its core is a ESP32.

The statement it complains about is in the M5Stack.h itself for the power off function.

If I try and compile in Arduino IDE and sketch that has the #include M5Stack.h, even on Example code in the "examples from Custom Library - M5Stack - Basic - Hello World, I get an compiling error.

Here is the error I get for Hello World with display to the TFT:
C:\Users\█████\Documents\Arduino\libraries\M5Stack\src\M5Stack.cpp: In member function 'void M5Stack::powerOFF()':

C:\Users\█████\Documents\Arduino\libraries\M5Stack\src\M5Stack.cpp:65:62: error: 'esp_sleep_enable_ext0_wakeup' was not declared in this scope

 esp_sleep_enable_ext0_wakeup((gpio_num_t)_wakeupPin , LOW);

Now I I have updated the library with GIT.

Arduino: 1.8.5 (Windows Store 1.8.10.0) (Windows 10), Board: "M5Stack-Core-ESP32

I can compile and run others like ResetReason.

So guidance would be helpful to resolve this