If it is the image attachment page, they have the body class attachment. So you can add the rule below in Main Options > Fonts & Custom > Custom CSS Rule box to hide the primary menu in them
@scrambler ‘s rule will just hide the menu. If you really don’t want the menu content in the HTML on the Attachement page (image.php), you’d have to build a child theme with a custom header.php which is where the menus get generated.