The Portfolio Archive pages are automatically generated from the Categories, Skills, and Tags that you enter into your individual portfolio items. When you are viewing a portfolio item on the front end, and click on a Category, Skill or Tag, you will be taken to a Portfolio Archive page, filtered to that Category, Skill or Tag.
These pages cannot be edited directly but can be styled and configured via the General Portfolio Options, found in the Theme Options at Avada > General Portfolio. Please see the Portfolio Theme Options doc for more details on what can be configured here. You can also add Sidebars to them in the Avada > Sidebars > Portfolio Archive tab in the Theme Options.
The items shown on the Archive pages pull their information from the individual Portfolio posts, including their Featured Image, Category, Skills, etc, so even if you are not displaying this information on the Single Portfolio Posts, it’s important it’s entered into the Portfolio tab of the Fusion Page Options on each Portfolio item, so all your Portfolio Posts are shown when filtering.