Hello @robinJiao
you are correct, M5Stack devices are feature rich ESP32 kits. And yes, you most likely can use the firebase-esp library to code for the ESP32 processor in your M5Core2. However the additional hardware, e.g. LCD, touch screen, RTC, accelerometer, etc. in your M5Core2 are not getting initialized automatically since the firebase-esp library doesn't know about them. That is the reason you are seeing a blank screen. (BTW: the firebase-esp code most likely is running though - did you check the serial output?)
That said, may I suggest you start with the libraries designed for M5Core2 and run some simple examples first? My apologies, if you already have done that.
Thanks
Felix