WordPress – Remove category from posts list and widget

The following code will help you remove a category from being displayed in your WordPress website:

/** Remove the private projects everywhere */
function globally_exclude_category( $wp_query ) {
     // Add the category to an array of excluded categories. In this case, though,
     // it's really just one.
     $excluded = array( '-84' );
     // Note that this is a cleaner way to write:
     $wp_query->set('category__not_in', $excluded);
     set_query_var( 'category__not_in', $excluded );
}
add_action( 'pre_get_posts', 'globally_exclude_category' );
function globally_exclude_category_widget($args){
     $exclude = "84";
     // The IDs of the excluding categories, comma separated 
     $args["exclude"] = $exclude;
     return $args;
}
add_filter("widget_categories_args", "globally_exclude_category_widget");