Codeigniter 3.x vs PHP 8.x

Hello,
I just updated my local server to PHP 8.x
After that I got several errors on my script that works fine on PHP 7.x
Its all concern about system folder codes.
For example I got this error:

Code:

A PHP Error was encountered
Severity: 8192

Message: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated

Filename: core/Output.php

Line Number: 457

And I think maybe some of you guys, prepared a functional version of system folder and wants to share it ?

( Or I need to pass back to PHP 7 and always work on here? Its not good for future )
Thanks a lot.