Create post index in WordPress

index.php

<?php
global $wp_query;
$page = ( get_query_var('paged') ) ? get_query_var('paged') : 1;
$ppp = get_query_var('posts_per_page');
$end = $ppp * $page;
$start = $end - $ppp + 1;

if (have_posts()): 
  while(have_posts()): the_post();

    printf('<h2 class="title">Index %s</h2>', str_pad($start, 2, "0", STR_PAD_LEFT));

    $start++
  endwhile;
endif; wp_reset_query();

the_posts_pagination(array(
  'prev_next' => true,
  'prev_text' => 'Previous',
  'next_text' => 'Next',
  'screen_reader_text' => '',
  'before_page_number' => '',
  'after_page_number' => '',
  'show_all' => false,
));