Thank you for fast you reply.
My first thought was that I did something wrong. For hours I've been looking for the fault. Until I realized that there is no fault. I would never have thought that it should look like this.
Is there a way to get the old style back?
I installed ProcessWire 3.0.103 and the Blog-module. All working fine. Only the configuration looks very ugly. I don't know if this your new style or an accident. I saw that better in the official video: https://www.youtube.com/watch?v=64XMGLuniqU
So it looks in my backend:
So it looks in the video: