How to drawColorBitmap on M5STACK Core2 in Arduino IDE / PlatformIO?

[swasi]

Hello everyone

I'm playing with my new Core2 and i saw the pretty display of the factory default.
Now i want to create my own Output on the LCD. I would like to drawColorBitmap like in the clock example of the factory default.

TFT_eSprite DisClockbuff = TFT_eSprite(&M5.Lcd);

void clockSetup()
{
    DisClockbuff.createSprite(164,101);
    DisClockbuff.drawJpg(clockImage,18401,0,0,163,101);
}

void clockFlush()
{
    uint16_t posx[6] = { 4, 28, 66, 90, 127, 144 };

    // colon between the numbers
    DisClockbuff.fillRect(0, 20, 162, 50, DisClockbuff.color565(0x1a, 0x11, 0x00));
    DisClockbuff.fillRect(0, 25, 2  , 45, DisClockbuff.color565(0xff, 0x9c, 0x00));

    DisClockbuff.fillRect(56,35, 5  , 5 , DisClockbuff.color565(0xff, 0x9c, 0x00));
    DisClockbuff.fillRect(56,54, 5  , 5 , DisClockbuff.color565(0xff, 0x9c, 0x00));

    DisClockbuff.fillRect(118,40, 5  , 5 , DisClockbuff.color565(0xff, 0x9c, 0x00));
    DisClockbuff.fillRect(118,57, 5  , 5 , DisClockbuff.color565(0xff, 0x9c, 0x00));

    M5.Rtc.GetTime(&sytState.Rtctime);
    
    // digits
    DisClockbuff.drawColorBitmap(posx[0],26,24,42,
                        DigNumber[ sytState.Rtctime.Hours / 10 ],
                        0xff9c00,
                        0x1a1100);
    DisClockbuff.drawColorBitmap(posx[1],26,24,42,
                        DigNumber[ sytState.Rtctime.Hours % 10 ],
                        0xff9c00,
                        0x1a1100);
    DisClockbuff.drawColorBitmap(posx[2],26,24,42,
                        DigNumber[ sytState.Rtctime.Minutes / 10 ],
                        0xff9c00,
                        0x1a1100);
    DisClockbuff.drawColorBitmap(posx[3],26,24,42,
                        DigNumber[ sytState.Rtctime.Minutes % 10 ],
                        0xff9c00,
                        0x1a1100);
    DisClockbuff.drawColorBitmap(posx[4],33,18,35,
                        DigNumber_35px[ sytState.Rtctime.Seconds / 10 ],
                        0xff9c00,
                        0x1a1100);
    DisClockbuff.drawColorBitmap(posx[5],33,18,35,
                        DigNumber_35px[ sytState.Rtctime.Seconds % 10 ],
                        0xff9c00,
                        0x1a1100);
    
    sytState.clockCount ++;
    sytState.clockCount %= 6;

    // this i don't know what it's for
    DisClockbuff.drawColorBitmap(0,0,164,17,
                            rectptrBuff[sytState.clockCount],
                            0xff9c00,
                            0x000000);

    // maybe this code will actually display the created image?
    DisClockbuff.pushSprite(72,4);
}

And yes, i know there is some more code for Image representation needed. I've added this to ask how it's working.

First i tried to remove a single digit. Then i registered that the code won't run on the device.
Can somebody please explain how this code is working?
Why can't i remove a single digit?
What is the minimum requirement to draw a single digit?