To register a new page layout in a custom theme, the developer needs to create a layouts.xml file in the app/design/frontend///Magento_Theme/layout directory. The layouts.xml file should contain the element with the id, label, and file attributes. The id attribute is used to reference the layout in other layout files, the label attribute is used to display the layout name in the admin panel, and the file attribute is used to specify the path to the layout file relative to the web directory of the theme. The app/design/frontend///layouts.xml and app/design/frontend///Magento_Theme/layouts.xml files are not valid and will not work. References: [Create a new page layout], [layouts.xml]

The styles-l.less and styles-m.less files are two main LESS files that are used to generate CSS files for different devices and screen sizes. The styles-l.less file is used to generate styles-l.css, which contains desktop-specific styles that are applied only when the screen width is greater than 768px. The styles-m.less file is used to generate styles-m.css, which contains basic and mobile-specific styles that are applied for all devices and screen sizes. The other options are not correct and do not reflect the purpose of these files. References: [Stylesheets], [Responsive web design]

To remove the default Wishlist and Compare Products blocks on a category page with layered navigation, the developer should place the modification in the app/design/frontend/Vendor/Theme/Magento_LayeredNavigation/layout/catalog_category_view_type_layered.xml file. This file is specific to the category pages with layered navigation and will override the default layout file from the Magento_LayeredNavigation module. The modification should use the tag with the name attribute specifying the name of the block and the remove attribute set to true. For example:

The app/design/frontend/Vendor/Theme/Magento_LayeredNavigation/layout/override/catalog_category_view_type_layered.xml file is not valid and will not work, as it is not a valid override path. The app/design/frontend/Vendor/Theme/Magento_Catalog/layout/catalog_category_view.xml file is not specific to the category pages with layered navigation and will affect all category pages. References: [Layout override], [Remove an element]