code: protected function updateVatDisplayMode(SaleInterface $sale)
      {
          // Vat display mode must not change if order has shipments or invoices.
          if ($sale->hasShipments() || $sale->hasInvoices()) {
              return false;
          }
  
          return parent::updateVatDisplayMode($sale);
      }
docs: @inheritDoc
  
  @param OrderInterface $sale