Hello, @Martine,
Yes, You can disable the full-width layout for the single product page by navigating to the Dashboard >> XSTORE >> Theme Options >> WooCommerce >> Single Product builder >> Layout, and from there disable the full-width option check the image: https://postimg.cc/DWFyRqn9
For the checkout page, there is no option in the theme to set the layout for this specific page it comes from WooCommerce and in this, there is no such feature like this as well.
Regards 8Themes Team.