on my M5Touch the touch screen is only working when powered on with USB power connected when i am using the UIFlow firmware. With other programs like Factory Test the touch is also working on battery power.

Problem is discussed in this thread: M5Paper / Touch only working on USB power

Thanks to the findings of @kinako and @felmue it seems that the I2C address of the GT911 touch controller is 0x5D or 0x14 depending if INT signal is high or low during initialisation. INT ist connected to GPIO36 wich is input only.

I can confirm that GT911 is using 0x14 when powered on via battery and 0x5D when powered on with USB connected.

The M5EPD library checks for both addresses:

Wire.beginTransmission(0x14);
if (Wire.endTransmission())
{
  Wire.beginTransmission(0x5D);
  if (Wire.endTransmission())
  {
    log_e("Touch screen IIC connection error");
    return ESP_FAIL;
  }
  _iic_addr = 0x5D;
}

It seems that the M5 UIFlow firmware is only initialising the 0x5D address.