Magento2 : Remove decimal from quantity

This decimal comes from database. So if you need to remove this, then you need to create column renderer. Here is an example

In your etc/module.xml file add sequence tag follows:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="[Vendor]_[Module]" setup_version="1.0.0">
         <sequence>
            <module name="Magento_CatalogInventory"/>
        </sequence>
    </module>
</config>

[Vendor][Module]/view/adminhtml/ui_component/product_listing.xml

<?xml version="1.0" encoding="UTF-8"?>
<listing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <columns name="product_columns" class="Magento\Catalog\Ui\Component\Listing\Columns">
        <column name="qty" class="[Vendor]\[Module]\Ui\Component\Listing\Columns\Quantity">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="filter" xsi:type="string">textRange</item>
                    <item name="add_field" xsi:type="boolean">true</item>
                    <item name="label" xsi:type="string" translate="true">Quantity</item>
                    <item name="sortOrder" xsi:type="number">75</item>
                </item>
            </argument>
        </column>
    </columns>
</listing>

Create a renderer [Vendor][Module]/Ui/Component/Listing/Columns/Quantity.php

namespace [Vendor]\[Module]\Ui\Component\Listing\Columns;

class Quantity extends \Magento\Ui\Component\Listing\Columns\Column
{
    /**
     * Column name
     */
    const NAME = 'column.qty';

    /**
     * Prepare Data Source
     *
     * @param array $dataSource
     * @return array
     */
    public function prepareDataSource(array $dataSource)
    {
        if (isset($dataSource['data']['items'])) {
            $fieldName = $this->getData('name');
            foreach ($dataSource['data']['items'] as & $item) {
                if (isset($item[$fieldName])) {
                    $item[$fieldName] = (int)$item[$fieldName];
                }
            }
        }

        return $dataSource;
    }
}

Create a renderer [Vendor][Module]/registration.php

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Vendor_Module',
    __DIR__
);