By default, the Magento 2.3.x GraphQL modules do not appear to reflect Catalog Price Rules
Copying the XML configuration files found in vendor/magento/module-catalog-rule/etc/webapi_rest/*.xml into a custom module in the etc/graphql area appears to resolve this issue:
# etc/graphql/events.xml
<?xml version="1.0"?>
<!--
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
<event name="catalog_product_get_final_price">
<observer name="catalogrule" instance="Magento\CatalogRule\Observer\ProcessFrontFinalPriceObserver" />
</event>
<event name="prepare_catalog_product_collection_prices">
<observer name="catalogrule" instance="Magento\CatalogRule\Observer\PrepareCatalogProductCollectionPricesObserver" />
</event>
</config>
# etc/graphql/di.xml
<?xml version="1.0"?>
<!--
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<type name="Magento\Catalog\Model\Product">
<plugin name="apply_catalog_rules_after_product_save_and_reindex" type="Magento\CatalogRule\Plugin\Indexer\Product\Save\ApplyRulesAfterReindex"/>
</type>
</config>
