Currently, you are set blog as simple post page that is why all blog post shows simple.
“aktuelles” this page is set as simple post page. You have to select blog template from Page attribute in this “aktuelles” page.
Follow below steps for set blog template set
Step 1. Go to Dashboard >> Page.
Step 2. Click Add New button.
Step 3. Select “Blog Full Width” template at right bottom of page
Step 4. Click publish button.