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

prepare_items.php

<?php
...
	/**
	 * Prepare the data for the WP List Table
	 *
	 * @return void
	 */
	public function prepare_items() {
		$columns               = $this->get_columns();
		$sortable              = $this->get_sortable_columns();
		$hidden                = array();
		$primary               = 'title';
		$this->_column_headers = array( $columns, $hidden, $sortable, $primary );
		$data                  = array();

		$this->process_bulk_action();

		$get_posts_obj = $this->get_posts_object();

		if ( $get_posts_obj->have_posts() ) {

			while ( $get_posts_obj->have_posts() ) {

				$get_posts_obj->the_post();

				$data[ get_the_ID() ] = array(
					'id'     => get_the_ID(),
					'title'  => get_the_title(),
					'type'   => ucwords( get_post_type_object( get_post_type() )->labels->singular_name ),
					'date'   => get_post_datetime(),
					'author' => get_the_author(),
				);
			}
			wp_reset_postdata();
		}

		$this->items = $data;

		$this->set_pagination_args(
			array(
				'total_items' => $get_posts_obj->found_posts,
				'per_page'    => $get_posts_obj->post_count,
				'total_pages' => $get_posts_obj->max_num_pages,
			)
		);
	}
  ...