manager-bundle/src/EventListener/InstallCommandListener.php
public function onConsoleTerminate(ConsoleTerminateEvent $event): void
    {
        if (!$event->getCommand() instanceof InstallCommand) {
            return;
        }

        (new Filesystem())
            ->copy(
                __DIR__.'/../Resources/skeleton/system/initialize.php',
                $this->projectDir.'/system/initialize.php',
                true
            )
        ;
    }
public function onConsoleTerminate(ConsoleTerminateEvent $event): void
    {
        if (!$event->getCommand() instanceof InstallCommand) {
            return;
        }

        (new Filesystem())
            ->copy(
                __DIR__.'/../Resources/skeleton/system/initialize.php',
                $this->projectDir.'/system/initialize.php',
                true
            )
        ;
    }
Adds the initialize.php file.