Hi,
where or how can I hide the itemToolbar, itemRatingBlock, itemLinks and the itemAuthorBlock? I looked in the global settings, but I didn't see it.

These options are located in the Category parameters under Item View options.
You have to know what is included inside those blocks to Hide. You won't find the options named like the block class, i.e. itemToolbar.
The itemToolbar block includes, for example, Font resizer, Print button, Email button, 'Social button' like ShareThis, AddThis etc., Anchor link to video, Anchor link to image gallery, Anchor link (with comments counter) to comment form.
If you Hide those then the itemToolbar will Hide.

Thank you :)

I have one more question. I have turn off / hiden the rrs icon in the view options and the global settings. But it still shows the rrs icon. Is there somewhere else I have to turn it ioff?

What K2 version do you use?
Do you use overrides?

2.6.6 with the polish language pack. No