Hey @MariMakes,
thanks for your tips, I tried them but could not yield better results unfortunately.
Something else I now noticed, which might be a source of error, is that the extruder is forming a loop of material instead of a straight line. This is visible when I'm actually trying to print my design but it's better even better visible in the step of material loading when the material is extruding out of the nozzle to make sure to push out the formerly used material.
This was the case for my self-made PCL (see-thru) but also for commercially-bought ABS (green), which I also tried.
Do you have an idea where this problem comes from and possibly also on how to solve it?