Let’s say if you need to get all the products through the collection with out-of-stock products and send it in JSON format then what will you do?

Step 1: Create a front controller GetProducts.php file

<?php

namespace MagemonkeysCustomInventoryControllerInventory;

use MagentoFrameworkAppActionContext;
use MagemonkeysCustomInventoryHelperData;


class GetProducts extends MagentoFrameworkAppActionAction
{
    public function __construct(
        Context $context,
        Data $helper
    ){
        $this->helper = $helper;
        parent::__construct($context);
    }

    public function execute()
    {
        $data = $this->helper->getProductData();

        header('Content-Type: application/json');

        echo json_encode(array(
            'data'=>$data,
            'meta'=> array(
                'count' => count($data)
            )
        ));

        return;

    }
}

Step 2: Create a Data.php in the helper folder of your module and paste the below code into it.

<?php

namespace MagemonkeysCustomInventoryHelper;

use MagentoFrameworkAppHelperAbstractHelper;
use MagentoFrameworkAppFilesystemDirectoryList;
use MagentoCatalogInventoryModelStockStockItemRepository; // Probably deprecating this with the following
use MagentoCatalogInventoryApiStockRegistryInterface;


class Data extends AbstractHelper
{
    private $productFactory;
    private $productCollectionFactory;
    private $stockItemRepository;
    private $inflightStatuses;
    protected $stockRegistry;


    public function __construct(
        MagentoCatalogModelProductFactory $productFactory,
        StockItemRepository $stockItemRepository, // Probably deprecating this with the following
        StockRegistryInterface $stockRegistry,
        MagentoCatalogModelResourceModelProductCollectionFactory $productCollectionFactory
    )
    {
        $this->inflightStatuses = array('processing', 'fulfillment_picking', 'incomplete', 'holded', 'on_review');
        $this->productFactory = $productFactory;
        $this->productCollectionFactory = $productCollectionFactory;
        $this->stockItemRepository = $stockItemRepository; // Probably deprecating this with the following
        $this->stockRegistry = $stockRegistry;
    }

    public function getProductData()
    {
        $data = array();

        $collection = $this->productCollectionFactory->create();
        $collection->addAttributeToSelect('*');
        $collection->setPageSize(100000);
        $collection->setFlag('has_stock_status_filter', false);


        /*echo $collection->count();
        exit;*/

        $collection->load();

        /* Start to add out of stock products in collection */
        $collection->clear();
        
        $updatedWhere = array();
        $where = $collection->getSelect()->getPart('where');
        foreach ($where as $key => $condition)
        {
            if(strpos($condition, 'stock_status_index.stock_status = 1') !== false){
                $updatedWhere[] = 'AND (stock_status_index.stock_status IN (1,0))';
            } else {
                $updatedWhere[] = $condition;
            }   
        }
        $collection->getSelect()->setPart('where', $updatedWhere);
        /* End of to add out of stock products in collection */

        $collection->load();

        foreach ($collection as $product) {

            $sku = trim($product->getSku());

            //$stockItem = $this->stockItemRepository->get($product->getId());
            $stockItem = $this->stockRegistry->getStockItemBySku($sku);


            $data[$sku] = array(
                'sku' => $sku,
                'name' => $product->getName(),
                'qty' => (int) $stockItem->getQty(),
                'in_stock' => $stockItem->getIsInStock()
            );
        }
        return $data;
    }
}