Magento – Magento 2.3.4 – infinite loop on checkout buttons

Create custom class & copy required functionality of vendor/magento/module-checkout/model/Session.php class file of Magento 2.3.3 version in it.

Then, use that custom class in Magento 2.3.4 version where you have added dependency of Magento\Checkout\Model\Session class file.

Or you can use '\Magento\Checkout\Model\Cart' class file to get all visible items of cart.

$this->cart->getCheckoutSession()->getQuote()->getAllVisibleItems();

Getting items directly from session was causing this error so I only got quote id from session and then used CartRepositoryInterface to retrieve items.

$session = $objectManager->get('\Magento\Checkout\Model\Session');
$quote_repository = $objectManager->get('\Magento\Quote\Api\CartRepositoryInterface');
$qid = $session->getQuoteId();
$quote = $quote_repository->get($qid);      
// retrieve quote items
$items = $quote->getAllItems();