Thanks for your answer and i'm happy that i am not the only dude, who have troubles with the engine.

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I use Nvidea Experience and have the latest drivers installed: 441.87 from 01/06/2020. I have a GTX 1070 Ti if this will help. But i don't think, that this card is to "crappy" for this engine.
Another idea, so i think that unity will have problems with my windows version?
I use Windows 10 Enterprise LTSC (Build 1809).
EDIT:
Problem solved!
I'm right, that the Problem was the Windows Version. I reinstalled another Windows 10 Edition (Windows 10 Enterprise / Build 1909) and now all buttons works fine.