I checked the wiring multiple times and actually also switched the dir and stp wire, but had the same result. Is it possible that only single gpios don't work for a reason e.g. the step gpio pin?
I have not a great knowledge about steppers so this question might seem a little dumb but is the frequency directly controlled by the delay time or is there an additional parameter that can be tuned? Because it just seems to me that the motor brings up the torque needed (I tried turning it by hand when it was running/but not moving and it held position quite sturdy), but maybe it misses to hold up the frequency of the controller.
Sadly I don't have an oscilloscope, only a multimeter..
Setting it up with the raspberry pi would take quite a while, I would have to set up the whole OS new, but I'll give it a try if I don't get this to work sooner..

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