You’ve provided the link of the Checkout page, not Cart page.
I’ve disabled Sidebar in Pages > Checkout page > selected Sidebar Position “Without Sidebar” in the “Page Layout” box on the right side.
Please check the Checkout page now and clear browser cache before.
Unfortunately we don’t have such possibility to disable sidebar for specific categories. It can be disabled for all categories though.
Please specify what buttons (on which pages) you want to change.