This gist is used in the tutorial https://www.vijayan.in/how-to-create-custom-table-list-in-wordpress-admin-page

get_sortable_columns.php

<?php
...
	/**
	 * Include the columns which can be sortable.
	 *
	 * @return Array $sortable_columns Return array of sortable columns.
	 */
	public function get_sortable_columns() {

		return array(
			'title'  => array( 'title', false ),
			'type'   => array( 'type', false ),
			'date'   => array( 'date', false ),
			'author' => array( 'author', false ),
		);
	}
  ...