Hey,
thanks for the quick and comprehensive reply. Unfortunately, I could not solve the problem yet.
There is no option to change the DirectX in my launcher and the right graphics card is enabled/displayed. Also, I can't find an option to downgrade my card driver.

The reason why it took me so long to answer is because I redownloaded the whole game by choosing the launchers repair option.

It still doesn't work. Does anyone know where to change the DiretX? It seems it's not supported for Mac..