I am using Opencart 3.0.2, I would like to simplify the checkout process by removing the steps and achieving something close to the one in this link https://www.opencart.com/index.php?rout ... _license=0 but without the ajax. Is it possible to do this by editing only the checkout files in catalog > view > theme > default ?
Checkout in OpenCart is built on JS with AJAX calls. To change this you will have to do a lot more than updating template files. But even then I'm not sure, how are you going to update info. Reload the page every time customer selects another payment/shipping method? Doesn't sound nice to me.
Actually, they ALL have JS. Providing, we're talking about full-featured checkout pages, not simplified ones, when you only enter email and hit enter.