Related_products_with_gridbuilder.php

function wpgb_wc_related_products( $query_args, $grid_id ) {

    global $product;

    // If it matches grid id 1, we set related product IDs.
    if ( 1 === $grid_id ) {

        $query_args['post_type'] = [ 'product' ];
        $query_args['post__in'] = wc_get_related_products( $product->get_id(), 8, $product->get_upsell_ids() );

    }

    return $query_args;

}

add_filter( 'wp_grid_builder/grid/query_args', 'wpgb_wc_related_products', 10, 2 );