create phtml file at

app/code/Magemonkeys/Custom/view/frontend/templates/index.phtml

<div id="ajax-response-id"></div>
<?php
$ajaxurl = $block->getAjaxUrl();
?>
<script type="text/x-magento-init">
        {
            "*": {
                "Magemonkeys_Custom/js/custom": {
                    "AjaxUrl": "<?php echo $ajaxurl; ?>",
                    "CurrentProduct": "<?php echo $currentProductId; ?>",
                }
            }
        }
</script>

create js file at

app/code/Magemonkeys/Custom/view/frontend/web/js/custom.js

define([
"jquery",
"jquery/ui"
], function($){
"use strict";

function main(config, element) {
var $elementvar = $(element);
var AjaxUrlcall = config.AjaxUrl;
var CurrentProduct = config.CurrentProduct;

$(document).ready(function(){
setTimeout(function(){
$.ajax({
context: '#ajax-response-id',
url: AjaxUrlcall,
type: "POST",
data: {currentproduct:CurrentProduct},
}).done(function (data) {
$('#ajax-response-id').html(data.output);
return true;
});
},1000);
});
};
return main;
});

Create a controller file at

app/code/Magemonkeys/Custom/Controller/Index/View.php

<?php
namespace MagemonkeysCustomControllerIndex; 
 
use MagentoFrameworkAppActionAction;
use MagentoFrameworkAppActionContext;
use MagentoFrameworkControllerResultJsonFactory;
use MagentoFrameworkViewResultPageFactory; 
 
class View extends Action
{ 
    protected $_resultPageFactory;
    protected $_resultJsonFactory;
 
    public function __construct(Context $context, PageFactory $resultPageFactory, JsonFactory $resultJsonFactory)
    { 
        $this->_resultPageFactory = $resultPageFactory;
        $this->_resultJsonFactory = $resultJsonFactory; 
        parent::__construct($context);
    }
 
    public function execute()
    {
        $result = $this->_resultJsonFactory->create();
        $resultPage = $this->_resultPageFactory->create();
        $currentProductId = $this->getRequest()->getParam('currentproduct');
         
        $data = array('currentproductid'=>$currentProductId);
 
        $block = $resultPage->getLayout()
                ->createBlock('MagemonkeysCustomBlockIndexView')
                ->setTemplate('Magemonkeys_Custom::view.phtml')
                ->setData('data',$data)
                ->toHtml();
 
        $result->setData(['output' => $block]);
        return $result;
    }
}

create block file at app/code/Magemonkeys/Custom/Block/Index/View.php

<?php
namespace MagemonkeysCustomBlockIndex;
 
use MagentoFrameworkViewElementTemplate;
 
class View extends Template
{
  public function __construct(TemplateContext $context, array $data = [])
    {
        parent::__construct($context, $data);
    }
 
  protected function _prepareLayout()
    {
        return parent::_prepareLayout(); 
    }
 
  public function getProducts($productId)
  {
     return;
  }
}

create phtml file  at app/code/Magemonkeys/Custom/view/frontend/templates/view.phtml

<?php
$productData = $block->getData();
$productId = $productData['data']['currentproductid'];
$products = $block->getProducts($productId);
?>
<div>
  <div>HTML codes</div>
</div>

that’s it.