// Custom WP Query with filters
$args = array(
    'post_type'      => 'product_variation',
    'posts_per_page' => 500,
);
$query = new WP_Query($args);

// Add custom join and where clause
add_filter('posts_join', 'custom_join_query');
add_filter('posts_where', 'custom_where_query');

// Fetch posts
$products = $query->get_posts();

// Remove filters after the query is executed
remove_filter('posts_join', 'custom_join_query');
remove_filter('posts_where', 'custom_where_query');

// Custom Join to get data from parent product and its meta
function custom_join_query($join) {
    global $wpdb;
    $join .= " LEFT JOIN {$wpdb->posts} AS parent ON parent.ID = {$wpdb->posts}.post_parent";
    $join .= " LEFT JOIN {$wpdb->term_relationships} AS rel ON rel.object_id = parent.ID";
    $join .= " LEFT JOIN {$wpdb->term_taxonomy} AS tax ON tax.term_taxonomy_id = rel.term_taxonomy_id";
    $join .= " LEFT JOIN {$wpdb->terms} AS term ON term.term_id = tax.term_id";
    $join .= " LEFT JOIN {$wpdb->postmeta} AS parent_meta ON parent_meta.post_id = parent.ID";
    return $join;
}

// Custom Where Clause to exclude certain categories, meta values, and stock status
function custom_where_query($where) {
    global $wpdb;
    $where .= " AND (term.slug NOT IN ('exclude-category-1', 'exclude-category-2'))"; // Exclude certain categories
    $where .= " AND (parent_meta.meta_key = '_stock_status' AND parent_meta.meta_value != 'onbackorder')"; // Exclude products on backorder
    return $where;
}

// Use $products as needed