Call custom section on page load customer/section/load/?sections=customsection

Question

I would like to call customer/section/load/?sections=customsection on page load. Similar how the cart is being called on page load.

I've already added section data in the frontend/di.xml

 <type name="Magento\Customer\CustomerData\SectionPoolInterface">
    <arguments>
        <argument name="sectionSourceMap" xsi:type="array">
            <item name="customsection" xsi:type="string">{Class}</item>
        </argument>
    </arguments>
</type>

However, the "customsection" is not being called unlike with "cart" and "quotecart"