If I understand you correctly you want the latest posts to appear inside the menu as sub menu items, is that correct? Something like this:
Category One top menu item
| Post A sub menu item
| Post B sub menu item
I have found this solution published here: https://alex.blog/2011/09/20/code-snippet-add-a-link-to-latest-post-to-wordpress-nav-menu/, and changed it so it not only replaces the URL of a menu item but also the title:
// Front end only, don't hack on the settings page
if ( ! is_admin() ) {
// Hook in early to modify the menu
// This is before the CSS "selected" classes are calculated
add_filter( 'wp_get_nav_menu_items', 'replace_placeholder_nav_menu_item_with_latest_post', 10, 3 );
}
// Replaces a custom URL placeholder with the URL to the latest post
function replace_placeholder_nav_menu_item_with_latest_post( $items, $menu, $args ) {
// Loop through the menu items looking for placeholder(s)
foreach ( $items as $item ) {
// Is this the placeholder we're looking for?
if ( '#latestpost' != $item->url )
continue;
// Get the latest post
$latestpost = get_posts( array(
'numberposts' => 1,
) );
if ( empty( $latestpost ) )
continue;
// Replace the placeholder with the real URL
$item->url = get_permalink( $latestpost[0]->ID );
// And also replace the title
$item->title = $latestpost[0]->post_title;
}
// Return the modified (or maybe unmodified) menu items array
return $items;
}
One would only need to loop through all placeholders #latestpost1
, #latestpost2
, and so on, and also change $latestpost
to get the last, second last, third last of a category.