Validate file if a select is...

If you upload a file, then information about it is in a separate array.
Use a request instance instead of $data.

PHP Code:

$file = Config\Services::request()->getFile('field_name');

if ($file !== null && $file->valid()) { // file uploaded without errors 
  // ....
} 


https://codeigniter.com/user_guide/libra...files.html