Detect product attributes after /product/%product%

function pm_detect_dynamic_product_attributes( $uri_parts, $request_url, $endpoints ) {
    global $wpdb, $permalink_manager_uris;

    // Make sure that no custom permalink was detected by Permalink Manager
    if ( ! empty( $pm_query['id'] ) ) {
        return $uri_parts;
    }

    // Make sure that $uri_parts variable is set correctly
    if ( empty( $uri_parts['uri'] ) ) {
        return $uri_parts;
    }

    // 1. Separate "product/%product%" from rest of URL
    preg_match( '/^(product\/[^\/]+)\/(.*)/', $uri_parts['uri'], $slugs );

    // 2. Check if any of slugs is a product attribute
    if ( ! empty( $slugs[2] ) ) {
        $found_attributes    = array();
        $possible_attributes = explode( "/", $slugs[2] );

        foreach ( $possible_attributes as $slug ) {
            $sql_query = "SELECT t.slug, t.term_id, tt.taxonomy FROM {$wpdb->terms} AS t INNER JOIN {$wpdb->term_taxonomy} AS tt ON(t.term_id = tt.term_id) WHERE 1=1 AND slug = %s";
            $term      = $wpdb->get_row( $wpdb->prepare( $sql_query, array( $slug ) ) );

            if ( ! empty( $term->taxonomy ) ) {
                $found_attributes[ $term->taxonomy ] = $term->slug;

                // OPTIONAL. Keep the below line to preselect the attribute in the add-to-cart form
                $_REQUEST["attribute_{$term->taxonomy}"] = $term->slug;
            }
        }

        // 3. Check if the product URI is a custom permalink
        $product_id = array_search( $slugs[1], $permalink_manager_uris );

        // 4. Change the final query if the post (product) is found
        if ( ! empty( $product_id ) ) {
            $post_object = get_post( $product_id );

            if ( ! empty( $post_object->post_type ) && $post_object->post_type == 'product' ) {
                $uri_parts['uri'] = $slugs[1];

                // You can use the $found_attributes array in your custom code
            }
        }
    }

    return $uri_parts;
}
add_filter( 'permalink_manager_detect_uri', 'pm_detect_dynamic_product_attributes', 20, 3 );