WordPress: Customize the number of posts displayed per Custom Post Type

functions.php

/**
 * Customize number of posts displayed per Custom Post Type
 *
 * @see https://mondaybynoon.com/wordpress-posts-per-page-per-custom-post-type/
 */
function custom_posts_per_page($query) {
  if(!is_admin()) {
    switch ($query->query_vars['post_type']) {
      case 'name_of_cpt1':
        $query->query_vars['posts_per_page'] = -1;
        break;
      case 'name_of_cpt2':
        $query->query_vars['posts_per_page'] = 20;
        break;
      default:
        break;
    }
  }
  return $query;
}
add_filter('pre_get_posts', 'custom_posts_per_page');