For the case I described above I decided to create a custom style with multiple symbol layers. The Data Combinations were "yes"-, "no"- and "partly"-strings.
For another case which was more complex with regard to the number of combinations I adopted the first advise. I copied the layer and created two symbologies, one hatching and one color filling. As proposed I converted the legend to a graphic, worked fine.
Thanks a lot for you help, done 😉