cpt archive post per page
add_filter( 'pre_get_posts', 'custom_change_portfolio_posts_per_page' );
/**
* Change Posts Per Page for Portfolio Archive.
*
* @param object $query data
*
*/
function custom_change_portfolio_posts_per_page( $query ) {
if ( $query->is_post_type_archive( 'portfolio' ) && ! is_admin() && $query->is_main_query() ) {
$query->set( 'posts_per_page', '6' );
}
return $query;
}