Default settings.php file references the no longer used admin theme centarro_claro

Installing centarro/commerce-kickstart-project (5.2.1)

Hi,
after the stupid Corona situation and alcohol withdrawal, I'm starting from scratch again.

Now that I've figured out how to trick Strato, or rather, how to make the server do what I want (which supposedly isn't possible), I have the following problem:

(I added the following code to the settings.php file: $config['system.logging']['error_level'] = 'verbose';)

The website encountered an unexpected error. Try again later.
TypeError: Drupal\Core\Extension\ThemeHandler::addTheme(): Argument #1 ($theme) must be of type Drupal\Core\Extension\Extension, null given, called in /.../htdocs/t-de/web/core/includes/theme.maintenance.inc on line 71 in Drupal\Core\Extension\ThemeHandler->addTheme() (line 91 of core/lib/Drupal/Core/Extension/ThemeHandler.php).
Drupal\Core\Extension\ThemeHandler->addTheme() (Line: 71)
_drupal_maintenance_theme() (Line: 267)
drupal_maintenance_theme() (Line: 103)
Drupal\Core\EventSubscriber\MaintenanceModeSubscriber->onMaintenanceModeRequest() (Line: 206)
Symfony\Component\EventDispatcher\EventDispatcher->callListeners() (Line: 56)
Symfony\Component\EventDispatcher\EventDispatcher->dispatch() (Line: 63)
Drupal\Core\EventSubscriber\MaintenanceModeSubscriber->onKernelRequestMaintenance() (Line: 246)
Symfony\Component\EventDispatcher\EventDispatcher::{closure:Symfony\Component\EventDispatcher\EventDispatcher::optimizeListeners():241}() (Line: 206)
Symfony\Component\EventDispatcher\EventDispatcher->callListeners() (Line: 56)
Symfony\Component\EventDispatcher\EventDispatcher->dispatch() (Line: 241)
Symfony\Component\HttpKernel\HttpKernel->handleThrowable() (Line: 91)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 32)
Drupal\big_pipe\StackMiddleware\ContentLength->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 54)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 745)
Drupal\Core\DrupalKernel->handle() (Line: 19)

The problem occurs when I activate maintenance mode on test2.tecmawi.de.
A genuine Drupal 11.3.6 installation doesn't produce this error in maintenance mode.
I'll compare the directories and files, copy them back and forth, test them, and share my solution.
However, since I'd rather move into production and it seems to be a fundamental problem, I'd prefer professional help.

See you later.