I want the shop to be displayed in full width (without a sidebar) and I have chosen this in the customizer as well. Nevertheless, some shop pages are displayed with sidebar, for example the product overview and the shopping cart as well as the cash register. So what can I do?
Another problem is that on the product overview no button is displayed, with which one can open the single product or put directly into the shopping cart. https://www.prokom-bw.de/shop/
The page you linked as your shop page seems to be a product archives page and not your main shop page.
You need to select your main shop page in WooCommerce settings in order to get it working full width and with the buttons.
Go to Woocommerce / Settings / Products tab and set your “Shop page” from the drop-down.
Do you have a product category called “bestellungen” – in some cases if the shop page URL and category URL matches (if the category URL base path is removed) then the two can conflict.
If you can provide a login to the site I can take a look and investigate further (if you send login details please make sure your reply is marked as private so only the site admins can see it)
For the cart and checkout page you can configure the full width layout on the edit page screen by choosing the right template http://prntscr.com/l7wepv
I have set it for you now for those 2 pages.
The Add to cart button is not present because an additional plugin you are using “WooCommerce Germanized” have an option which overrides the default look of the theme. Uncheck this option and the Add to cart button will show on the shop page http://prntscr.com/l7wu5v