Custom Error Pages
As of Joomla 5.0 the default Cassiopeia template can now be customised to support custom 404 and 403 pages.
There are two new module positions available (error-403 and error-404) which will add content to the error.php file of the template to replace the default message depending on it being a 403 (forbidden) or 404 (not found) error.
The existing error page text is displayed if there is no module and if debug is enabled then the debug information is still displayed below the module.