Magento2 Create Customer Checkout Quote and Add Products to that Quote

Here we will learn, how in Magento2 Create Customer Checkout Quote and Add Products to that Quote.

I have created a demo class here:

<?php
namespace Webkul\Test\Model;

class CustomAddToCart
{
   public function __construct(
     \Magento\Catalog\Model\ProductFactory $productFactory,
     \Magento\Customer\Model\Session $customerSession,
     \Magento\Quote\Api\CartManagementInterface $quoteManagement,
     \Magento\Quote\Api\CartRepositoryInterface $quoteRepository
   ) {
     $this->productFactory = $productFactory;
     $this->quoteManagement = $quoteManagement;
     $this->quoteRepository = $quoteRepository;
     $this->_customerSession = $customerSession;
   }

   public function quoteAddToCart()
   {
      $customerId = $this->_customerSession->getCustomerId();
      // let's assume product Id is 50
      $product = $this->productFactory->create()->load(50);
      $params = [
            "product": "50",
            "qty": "1",
            "options": [ //if product has options
                "4": "8",
                "5": "10",
            ]
        ];
      $request = new \Magento\Framework\DataObject();
      $request->setData($params);
      // here quote is created for customer
      $quoteId = $this->quoteManagement->createEmptyCartForCustomer($customerId);
      $quote = $this->quoteRepository->get($quoteId);
      $quote->addProduct($productAddToCart, $request);
      $this->quoteRepository->save($quote);
      $quote->collectTotals();
         
   }
}

In above snippet you can see i have created the quote by customer id using
createEmptyCartForCustomer() method, it will return new Quote Id.