On the new checkout page the cart is fixed, you can’t see it until the final step, at which point if you want to change sometime because you didn’t notice it before, there is no obvious place to change it. There should be an “edit cart” button on the final “review and place order” step that takes them back to the cart page.
Otherwise they need to click the shopping cart drop down and click “view cart”. Since that isn’t directly visible, and even if it was the customer is thinking “edit” not “view”, it really needs that button.
I agree. I have had frustrated customers who can’t edit the cart on checkout. They don’t expect to have to click on the cart icon in the upper left to edit their cart and end up not purchasing.