After some tests I am back to zero. I installed pi-desktop-base-1.1.0.deb on OSMC. (Thx dillthedog). But my Raspberry Pi3 which is build in the nice case (Pi Desktop) from element14 doesn’t react on the on/off power button. I should be able to switch of the RPi via OSMC software button and switch on again on hardware button.
In Raspbian it works. Why not on OSMC which uses the same type of software in the background. Someone an idea how to continue?