Upgrade View Parser
Documentations
What has been changed
- You have to change the implementation and loading of the Parser Library. 
- The Views can copied from CI3. Usually no changes there are required. 
Upgrade Guide
- Wherever you use the View Parser Library replace - $this->load->library('parser');with- $parser = service('parser');.
- You have to change the render part in your controller from - $this->parser->parse('blog_template', $data);to- return $parser->setData($data)->render('blog_template');.
Code Example
CodeIgniter Version 3.x
<?php
$this->load->library('parser');
$data = array(
    'blog_title'   => 'My Blog Title',
    'blog_heading' => 'My Blog Heading'
);
$this->parser
    ->parse('blog_template', $data);
CodeIgniter Version 4.x
<?php
$parser = service('parser');
$data = [
    'blog_title'   => 'My Blog Title',
    'blog_heading' => 'My Blog Heading',
];
return $parser->setData($data)->render('blog_template');