If you want to show product listing in a given order by its category in the Catalog Product List Widget? Then follow the below steps.

Step 1: Create a file like ProductOrder/CatalogProList/etc/frontend/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="MagentoCatalogWidgetBlockProductProductsList">
        <plugin name="custom_widgets_product_list" type="ProductOrderCatalogProListPluginBlockProductProductsOrderList"/>
    </type>
</config>

Step 2: Create another file like ProductOrder/CatalogProList/Plugin/Block/Product/ProductsOrderList.php

<?php    
	namespace ProductOrderCatalogProListPluginBlockProduct;

	use MagentoCatalogModelResourceModelProductCollection;
	use MagentoCatalogWidgetBlockProductProductsList;

	/**
	 * Class ProductsOrderList
	 */
	class ProductsOrderList
	{

	    /**
	     * @param ProductsList $subject
	     * @param Collection $result
	     * @return Collection
	     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
	     */
	    public function afterCreateCollection(ProductsList $subject, Collection $result)
	    {
	        $result->getSelect()->order('cat_index_position asc');

	        return $result;
	    }
	}

That’s it…

Now, you can check your widget’s products. It will be displayed as per the given order.