@spruce_m00se Thanks for the tipp with den capacitator. I solderd one directly to 5V/Ground inputs of the LCD-driver board. Now the heat is going down.
It's a 2,2nF ceramics caps.
The impedance produces a bit of heat. As I power the Pi0, an I2S, an USB hub and the LCD from the same powerline... there was some ripple in the impedance next to the 3,3V regualtor.