nightmystic1981

Its resolved. It was not a CSS issue at all.
In fact it was not an issue at all.
It was the way the Theme works, It shows the headlines and content.
When I clicked on the headline the post appeared with the image and button.
So if I want the image and button to appear immediately, I would have to make a page instead of posts.

Okay, the Shopstar Theme works.
Some other themes like the Hello theme for woocommerce also did not work.
The problem probably lies somewhere in the CSS code, but I am a beginner and do not know how to find the issue in the code.
If anyone is interested in finding out I would very much appreciate it.
If I accidently solve it myself, I will let you know.

Update:
It does work when I change to the twenty nineteen theme

Ive done some more testing.
I completely removed the website. Installed version 5.5.3 instead of 5.6.
Added an image and a button to the post Hello World.
It worked just fine.
Now I change Theme and the image and button are gone.
I change back to a default WordPress theme twentytwentyone.
Button and image still gone.