Add custom block on listing page : Magento2

You can do that if you create new module to override this block: vendor\magento\module-catalog\Block\Product\ListProduct.php

to override this block, you need to create di.xml at app\code\Vendor\Module_Name\etc

di.xml content:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Catalog\Block\Product\ListProduct" type="Vendor\Module_Name\Block\Product\ListProduct" />
</config>

Create new file name ListProduct.php at app\code\Vendor\Module_Name\Block\Product

ListProduct.php content:

namespace Vendor\Module_Name\Block\Product;
class ListProduct extends \Magento\Catalog\Block\Product\ListProduct
{
    public function getProductDetailsHtml(\Magento\Catalog\Model\Product $product)
    {
        $html = $this->getLayout()->createBlock('Magento\Framework\View\Element\Template')->setProduct($product)->setTemplate('Vendor_ModuleName::test.phtml')->toHtml();
        $renderer = $this->getDetailsRenderer($product->getTypeId());
        if ($renderer) {
            $renderer->setProduct($product);
            return $html.$renderer->toHtml();
        }
        return '';
    }
}

You can change block Magento\Framework\View\Element\Template to your block

create test.phtml file at app\code\Vendor\Module_Name\view\frontend\templates

Currently you cannot do this because all logic of product output is hardcoded in list.phtml template.

Here is my take on the solution - but you must modify the list.phtml template:

catalog_category_view.xml

<referenceBlock name="category.products.list">
    <block class="Magento\Catalog\Block\Product\ProductList\Item\Container" name="custom.block.container" as="custom-block-container">
        <block class="Magento\Catalog\Block\Product\ProductList\Item\Block" name="custom.block" as="custom-block"
           template="Magento_Catalog::product/view/custom-block.phtml" />
    </block>
</referenceBlock>

In custom-block.phtml you can get the product like this:

$_product = $block->getProduct();

You will need to overwrite the list.phtml template though... Just add this where you want your custom block to show:

<?php if ($customBlock = $block->getChildBlock('custom-block-container')): ?>
    <?= $customBlock->setProduct($_product)->getChildHtml() ?>
<?php endif; ?>

If you really want to avoid modifying the list.phtml template, then you might be able to do a similar thing but in a different template.