This error happens because Joomla 5 requires PHP 8.1+, but you have an outdated third-party extension or template containing the create_function() function. The PHP development team deprecated this function in PHP 7.2 and completely removed it in PHP 8.0.0. When Joomla runs on modern PHP, encountering this removed function instantly triggers a fatal crash.
How to fix the problem
- Choose a compatible version of PHP - likely PHP 7.2
- You should be able to access the Admin and front end again. Migrate Joomla to the current version and update all templates and plugins.
