Entities like Products have panels for Files, Attributes, and other items. The panels disappear for the user after clicking on X in the top-right corner of the panel.
How to restore the panels after they have been hidden?
You should be able to bring it back by clicking on its tab at the top of the screen. For example, if you closed the Attribute Values panel, then clicking on the Attribute Values tab at the top of the screen will bring it back.