Hi @ulf01,
Thank you for reaching out.
I understand you’re new to WooCommerce and using the Gutenberg editor. I’ll be happy to help you out navigate through our platform.
how I can re-insert the cross-sell and up-sell block in the cart layout once they are deleted and
To re-insert the cross-sell block, navigate to the ‘Blocks’ menu in the Gutenberg editor. There, you will find the Cart Cross Sells blocks. Click on it to add it to your cart layout. Here’s a short video for explanation.
how I can modify the column-structure of the cart block, e.g. switch to full width?
For modifying the column structure, you would need to use the ‘Columns’ block. Add this block to your layout and adjust the settings to your preference. To switch to full width, you need to click on the block and then find the settings on the right-hand side of your block editor to choose the correct settings of your choice. You can find more details from this guide.
Also I wonder how to make the Cart Line Items-block simpler (just 2-3 lines per product )
To make the Cart Line Items block simpler, you can use the block settings on the right to select the number of products to show. In most cases, some of the cart blocks are blocked to avoid changes using the block editor, thus, changes can only be achieved with the help of a custom code snippet. You can read more on locked blocks here. More details on customizing the cart block can be found here.
in addition I liked the cart to use the width available on the screen, so reduce the side margins.
In mos cases, the cart uses the width available of the screen, however, you can adjust the ‘Width’ further with the help of custom CSS code. Please note that customization requests are out of our support scope.
You can find more details on customizing your cart from the following guides:
I hope this helps.