CODE EXAMPLE FOR PHP

Change COD default order status to “On Hold” instead of “Processing” in Woocommerce

add_filter( 'woocommerce_cod_process_payment_order_status', 'change_cod_payment_order_status', 10, 2 );
function change_cod_payment_order_status( $order_status, $order ) {
    return 'on-hold';
}