Yes, correct, I forgot mentioning the textures.
I copied the folder \texture.CIRP of CIRP_Hovercraft_2019.zip. In there is a file called "prop_srn.bmp" but no success.
As I mentioned I'm not a specialist in creating AI models, this was just for my own use.
P.S.
This problem already existed in FSX which I just checked but I wasn't aware of it anymore.