Custom edit post column – category not showing

Here I tested this code and its working fine and steps here.

1. I am just creating a dummy custom_post_type here book with the following code.

    function kv_custom_post_books() {
      $args = array(
       'public' => true,
       'label'  => 'Books',
       'taxonomies' => array('category', 'post_tag') , 
       'supports'           => array( 'title', 'editor', 'thumbnail' )
     );
    register_post_type( 'book', $args );
   }
   add_action( 'init', 'kv_custom_post_books' );
   

Here i am not sure, you used this line. 'taxonomies' => array('category', 'post_tag') . This one gets you the default categoires to your custom post type.

2. Now we will rewrite your action hook here. and we use the same functions no change in it.

   add_filter('manage_edit-book_columns', 'custom_columns', 10);  
   add_action('manage_posts_custom_column', 'custom_columns_thumb', 10, 2);  
   
   function custom_columns($columns) {         
      $columns = array(
         'cb' => '<input type="checkbox" />',
         'title' => 'Title',
         'categories' => 'Categories', // not showing
         'thumb' => __('Thumb'),
         'date' => __( 'Date' )
      );
     return $columns;
   }  
   
   function custom_columns_thumb($column_name, $id){  
     if($column_name === 'thumb') {  
         echo the_post_thumbnail( 'thumb' );  
     }  
   }
   

Note : I just edited only one line in your code. add_filter('manage_edit-book_columns', 'custom_columns', 10);. We have to specify your custom post type in your action hook. This is the ultimate thing here . manage_edit-book_columns Instead of default one we have to specify the custom post type name here.

Here I attached a screenshot for you,