Related Tags Concept

You can use simple solution below. You need to use this function in the loop. You can collect tags/categories in an array or show tags/categories under the posts.

$terms = get_the_terms( get_the_ID(), 'category' );
  if ( $terms && ! is_wp_error( $terms ) ) : 
   $catlinks = array();
    foreach ( $terms as $term ) {
      $catlinks[] = $term->name;
    }

$catso = join( ", ", $catlinks );
?>

<p class="list-of-cats">
    <?php printf( esc_html__( 'Categories: <span>%s</span>', 'textdomain' ), esc_html( $catso ) ); ?>
</p>