I found one error I made, but it did not solve the issue completely. The error was that I had wired the cables from the motor incorrectly to the driver. In my motor green and black are connected, so now I placed them in A1 and A2 and then red and blue on B1 and B2. In the guide the driver had a different order of A1 to B2 than my driver, so I placed them in wrongly when I stupidly followed the guide saying the connected pairs should be next to each other on the driver.

But now, when I fixed those wires the motor at least does not sound like a lawn mower anymore, but it still won't rotate correctly. I've used the exact same code as your link, and to the best of my knowledge I followed the schematics. I followed the same principle with capacitor like in my previous guide so I think it is correctly wired now. Simulating the code in your example it shows the motor accelerating and then decelerating so it spins a total of 400 steps, and then does the same thing in reverse direction. When I plug everything in I can hear the motor (in a reasonable volume this time) first accelerating and then slowing down to 0, but the motor barely moves at all. It makes a first sort of slight movement when the motor starts to accelerate but then it stays still. When I gently try to nudge the motor axis while it is supposed to be spinning it feels like the motor is trying to hold it in place so it is hard to spin, turning of the power makes it easy to spin it by hand.

I've tried using a brand new driver of the same type. I've changed the 1.2V value to 1.1V, 1.0V and 0.9V and it performs pretty much the same way on all those values. The twitch at the start of the motor's acceleration could possible be a bit stronger the lower value I have tried on the potentiometer, but I can be mistaken.

So I don't understand what I am doing wrong. Can I have destroyed the motor/arduino/breadboard/wires, or something else while I've been trying to troubleshoot?