This is for people with large codebases who are limited in moving to newer/safer/faster PHP versions only due to the fact that undefined array keys or undefined variables are now warnings in PHP 8.

To suppress undefined-warnings in PHP 8, I have found two main approaches: using a custom error handler with a PHP extension (some C-code) or setting a custom error handler (php-code) in an auto_prepend_file via php.ini.

Run the code with these tweaks until you have time to fix or rewrite that massive codebase.