For required form fields, is there a way to have a section on the page listing all inputs where there is an issue instead of the pop-ups that appear one by one on the page?
The “pop ups” are validation error warnings on HTML5 form elements by your browser, not Webflow. Webflow does not have form validation as a feature on the server side available to your site so you are stuck with the default element alerts or you could wire up a client side validation library which might offer more control. I personally use the formvalidation.io library. It is a licensed product.