Steps to reproduce the issue

One of the reasons to enable the System - Debug plugin is for debugging - the problem is that it doesnt actually load on a page that is an error page!

To replicate, login to Joomla 4 admin and enable the System - Debug plugin

Then create a PHP error (easy to do, edit administrator/components/com_cpanel/src/Controller/DisplayController.php and add

Factory::isAdmin();

after

public function display($cachable = false, $urlparams = array())
{

Then visit Home Dashboard menu item

Expected result

Same as the actual result below - but with the debug toolbar at the bottom as well so that the request can be inspected.

Actual result

System information (as much as possible)

Joomla 4 beta 1

Additional comments