There are different reasons you would want to remove the currency switcher dropdown from Magento 2 storefront.
For example, you may want to remove it because you use Magento 2 Automatic Currency Switcher and don't want to allow customers to manually change a currency.
In order to remove the currency switcher dropdown follow these steps:
1. Create a new file inside your storefront theme folder:
app/design/frontend/ThemeVendor/ThemeName/Magento_Theme/layout/default.xml
2. Add this code into it:
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="currency" remove="true" />
<referenceBlock name="store.settings.currency" remove="true" />
</body>
</page>
In case you already have Magento_Theme/layout/default.xml file, then edit it and put this code before </body> closing tag:
<referenceBlock name="currency" remove="true" />
<referenceBlock name="store.settings.currency" remove="true" />
3. Flush Magento cache, run CLI command:
bin/magento c:f
That's all :-)