Add custom option Programmatically in cart its not increasing quantity in cart

I am adding custom option programatically in below observer.

<event name="checkout_cart_product_add_after">
 <observer name="mymodule_checkout_cart_product_add_after" instance="ExtendStripeSubscriptionObserverCheckoutCartProductAddAfterObserver" />
</event>

and observer code in below file its not increasing quantity in same cart item , its showing separate products in cart.

<?php
namespace ExtendStripeSubscriptionObserver;

use MagentoFrameworkEventObserver as EventObserver;
use MagentoFrameworkEventObserverInterface;
use MagentoFrameworkSerializeSerializerInterface;

class CheckoutCartProductAddAfterObserver implements ObserverInterface
{
    /**
     * @var MagentoFrameworkViewLayoutInterface
     */
    protected $_layout;
    /**
     * @var MagentoStoreModelStoreManagerInterface
     */
    protected $_storeManager;
    protected $_request;
    
    /**
     * @var SerializerInterface
     */
    protected $serializer;
    
    /**
     * @param MagentoStoreModelStoreManagerInterface $storeManager
     * @param MagentoFrameworkViewLayoutInterface $layout
     */
    public function __construct(
        MagentoStoreModelStoreManagerInterface $storeManager,
        MagentoFrameworkViewLayoutInterface $layout,
        MagentoFrameworkAppRequestInterface $request,
        SerializerInterface $serializer
    )
    {
        $this->_layout = $layout;
        $this->_storeManager = $storeManager;
        $this->_request = $request;
        $this->serializer = $serializer;
    }
    /**
     * Add order information into GA block to render on checkout success pages
     *
     * @param EventObserver $observer
     * @return void
     */
    public function execute(EventObserver $observer)
    {
        /* @var MagentoQuoteModelQuoteItem $item */
        $item = $observer->getQuoteItem();
        $additionalOptions = array();
        $additionalOptions[] = [
                    'label' => 'Repeats Every',
                    'value' => '1 Month'
                ];
        if(count($additionalOptions) > 0)
        {
            $item->addOption(array(
                'code' => 'additional_options',
                'value' => $this->serializer->serialize($additionalOptions)
            ));
        }
        /* To Do */
        // Edit Cart - May need to remove option and readd them
        // Pre-fill remarks on product edit pages
        // Check for comparability with custom option
    }
}