Add Static Page to Reading Settings for Custom Post Type

Is there a way to add another static page option to the reading settings page?

Yes.

Code:

/** * Adds a custom field: "Projects page"; on the "Settings > Reading" page. */add_action( 'admin_init', function () {    $id = 'page_for_projects';    // add_settings_field( $id, $title, $callback, $page, $section = 'default', $args = array() )    add_settings_field( $id, 'Projects page:', 'settings_field_page_for_projects', 'reading', 'default', array(        'label_for' => 'field-' . $id, // A unique ID for the field. Optional.        'class'     => 'row-' . $id,   // A unique class for the TR. Optional.    ) );} );/** * Renders the custom "Projects page" field. * * @param array $args */function settings_field_page_for_projects( $args ) {    $id = 'page_for_projects';    wp_dropdown_pages( array(        'name'              => $id,        'show_option_none'  => '— Select —',        'option_none_value' => '0',        'selected'          => get_option( $id ),    ) );}/** * Adds page_for_projects to the white-listed options, which are automatically * updated by WordPress. * * @param array $options */add_filter( 'whitelist_options', function ( $options ) {    $options['reading'][] = 'page_for_projects';    return $options;} );

Preview:

Also, is there a way to mark the selected page like this in Pages?

Yes.

Code:

/** * Filters the post states on the "Pages" edit page. Displays "Projects Page" * after the post/page title, if the current page is the Projects static page. * * @param array $states * @param WP_Post $post */add_filter( 'display_post_states', function ( $states, $post ) {    if ( intval( get_option( 'page_for_projects' ) ) === $post->ID ) {        $states['page_for_projects'] = __( 'Projects Page' );    }    return $states;}, 10, 2 );

Preview:

And if you must or need to, you can use JavaScript/jQuery to move the "Projects page" field to below the "Posts page" in the "Your homepage displays" column.