Magento 2 Discount Label and Amount are not showing on checkout cart summary?

/vendor/magento/module-sales-rule/view/frontend/layout/checkout_cart_index.xml

Take below code from above file

<item name="discount" xsi:type="array">
   <item name="component" xsi:type="string">Magento_SalesRule/js/view/cart/totals/discount</item>
   <item name="config" xsi:type="array">
    <item name="title" xsi:type="string" translate="true">Discount</item>
   </item>
</item>

Insert it in checkout_cart_index.xml file of Magento_checkout in your theme by Overriding it there.

Now you can see discount there.