wp set posts per page archive

//cpt == your own custom post type

function set_posts_per_page_cpt( $query ) {
  if ( !is_admin() && $query->is_main_query() && is_post_type_archive( 'cpt' ) ) {
    $query->set( 'posts_per_page', '10' );
  }
}
add_action( 'pre_get_posts', 'set_posts_per_page_cpt' );