All right I got it now!! In the new version, you have to click on the three dots next to the wheel on the upper right corner. And then you can click on “Ansicht anpassen” which is German and should be something like “screen options” and THERE you have the option to make the feature image option visible.. Thank you word press for being so complicated!

Thank you CG! You helped me a lot!

Hello cg, thank you for your fast response! I don’t know where to find the menu, you show in your picture! Do you have hint for more, where I could locate it? Thank you very much!