Hi,
I think it's because a subscriber with the "kernel.exception" event should use Symfony\Component\HttpKernel\Event\ExceptionEvent instead of Symfony\Contracts\EventDispatcher\Event and according to
this page →
using Symfony\Contracts\EventDispatcher\Event can lead to fatal errors.
In addition, $exception = $event->getException(); should be replaced by $exception = $event->getThrowable(); in BrokenLinkSubscriber.php line 45 because the method getException () is deprecated since symfony 4 and trigger a fatal error in D10.
I worked on a patch and it seems to work on my local D10 environment.