PHP Filtro

functions.php

add_action( 'pre_get_posts', 'query_filter_category' );

function query_filter_category( $query ) {
	if ( $_GET && isset( $_GET['tid'] ) && $query->is_main_query() ) {
		$tid = $_GET['tid'];
		$tids = [];
		$tax_query = ['relation' => 'OR'];
		global $wpdb;
		foreach($tid as $t):
			$result = $wpdb->get_results( 'SELECT object_id FROM ' . $wpdb->prefix . 'term_relationships WHERE term_taxonomy_id = ' . $t );
			if ( $result ) {
				foreach($result as $r):
					$tids[] = $r->object_id;
				endforeach;
			}
			//$tax_query[] = [ 'taxonomy' => 'product_cat', 'field' => 'term_id', 'terms' => $t ];
		endforeach;

		$query->set('post__in', $tids);
	}

	return $query;
}