Very strange.
This empty space is a cart drawer element (it has visibility: hidden, so invisible, but takes space). Later it’s hidden by a CSS rule, but it’s at the bottom of the file and loads later:
So your theme must have Cart type set to drawer.
But it does not load a stylesheet for cart drawer (component-cart-drawer.css) and does not show it at all – customers are redirected to cart page.
These parts of theme code are missing – https://github.com/Shopify/dawn/blob/main/layout/theme.liquid#L261-L267 and https://github.com/Shopify/dawn/blob/main/layout/theme.liquid#L372-L374
Not sure why it was done. Restoring them would most probably fix your problem. Or simply change from “Drawer” to “Page” in “Theme settings”=> “Cart”