Display out of stock product only for specific Category in Magento2

To do above things, you need to do this things.

1. Vendor\Extension\etc\di.xml

<type name="Magento\CatalogInventory\Helper\Stock">
    <plugin name="Vendor_Extension_Stock_Helper" type="Vendor\Extension\Plugin\Helper\Stock" sortOrder="10" disabled="false"  />
</type>

2. Create the Helper File with arround plugin.

Vendor\Extension\Plugin\Helper\Stock.php

<?php
namespace Vendor\Extension\Plugin\Helper;

class Stock
{    
    public function aroundAddIsInStockFilterToCollection(\Magento\CatalogInventory\Helper\Stock $subject, \Closure $proceed, $collection)
    {
       // Do your Logic Here
        return $returnValue;
    }
}

You should extend the original function ( Magento\CatalogInventory\Model\ProductCollectionStockCondition::apply() ) which is checking the stock configuration.

"Display out of stock products" config in store > Config > catalog > inventory.

You can use preference to extend that apply() function and add additional condition like that.

from:
$this->stockHelper->addIsInStockFilterToCollection($collection);

to:
if(in_array(category_id, ur_list_of_ids))
$this->stockHelper->addIsInStockFilterToCollection($collection);

In this way, you can enable out of stock products in some of the category only.