Being picky, the PHPMailer.php is clearly somewhere, but you don't show the folder name.
The big clue that I see is that you require
"/opt/bitnami/apache2/htdocs/application/third_party/phpmailer/src/PHPMailer.php",
but you chmod'd
"/opt/bitnami/apache2/htdocs/sub_crud/application/third_party/phpmailer/src/PHPMailer.php".
Do you spot the difference between them? I even indented the above to make it easier to see :-O
Could your DOCUMENT_ROOT be set wrong?