well…again I solved it myself. I only connected the ground, but didn’t separate out 5v and 3.3v on the board. So I desoldered the chip using my heatgun, scratched out the link between pin 1 and pin 16, resoldered the chip on the board, then at C8 (c5) on my board I scratched out the link tot pin 16, thus completely isolating pin 16. Then I connected pin 1 to C8 again for 5v.
Lastly I mounted 1 100nf decoupling cap on the GND at one side and on pin 16 on the other side. Also I connected p16 to 3.3v.
Now it works.
Too much jank for me. I ordered the Adafruit HX711 board, which supports 3.3v out of the box.
However, it does work now.