With active admin theme Gin I see the warning message in the dblog when trying to add a new block using the Layout Builder:
Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in Drupal\Core\Template\TwigExtension->withoutFilter() (line 657 of /app/web/core/lib/Drupal/Core/Template/TwigExtension.php)
#0 /app/web/core/includes/bootstrap.inc(347): _drupal_error_handler_real(8192, 'explode(): Pass...', '/app/web/core/l...', 657)
#1 [internal function]: _drupal_error_handler(8192, 'explode(): Pass...', '/app/web/core/l...', 657)
#2 /app/web/core/lib/Drupal/Core/Template/TwigExtension.php(657): explode('.', NULL)
#3 /app/vendor/twig/twig/src/Environment.php(418) : eval()'d code(48): Drupal\Core\Template\TwigExtension->withoutFilter(Array, NULL)
#4 /app/vendor/twig/twig/src/Template.php(405): __TwigTemplate_26818864b4f252bdbef5d300ee452184->doDisplay(Array, Array)
#5 /app/vendor/twig/twig/src/Template.php(378): Twig\Template->displayWithErrorHandling(Array, Array)
#6 /app/vendor/twig/twig/src/Template.php(390): Twig\Template->display(Array)
#7 /app/web/core/themes/engines/twig/twig.engine(55): Twig\Template->render(Array)
#8 /app/web/core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/contrib/...', Array)
#9 /app/web/core/lib/Drupal/Core/Render/Renderer.php(433): Drupal\Core\Theme\ThemeManager->render('page', Array)
#10 /app/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false)
#11 /app/web/core/lib/Drupal/Core/Template/TwigExtension.php(479): Drupal\Core\Render\Renderer->render(Array)
#12 /app/vendor/twig/twig/src/Environment.php(418) : eval()'d code(87): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true)
#13 /app/vendor/twig/twig/src/Template.php(405): __TwigTemplate_258cae9c29f5ecac1f3715050cc1e393->doDisplay(Array, Array)
#14 /app/vendor/twig/twig/src/Template.php(378): Twig\Template->displayWithErrorHandling(Array, Array)
#15 /app/vendor/twig/twig/src/Template.php(390): Twig\Template->display(Array)
#16 /app/web/core/themes/engines/twig/twig.engine(55): Twig\Template->render(Array)
#17 /app/web/core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/contrib/...', Array)
#18 /app/web/core/lib/Drupal/Core/Render/Renderer.php(433): Drupal\Core\Theme\ThemeManager->render('html', Array)
#19 /app/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false)
#20 /app/web/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(162): Drupal\Core\Render\Renderer->render(Array)
#21 /app/web/core/lib/Drupal/Core/Render/Renderer.php(580): Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}()
#22 /app/web/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(163): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#23 /app/web/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php(90): Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\CurrentRouteMatch))
#24 [internal function]: Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#25 /app/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(142): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#26 /app/vendor/symfony/http-kernel/HttpKernel.php(174): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view')
#27 /app/vendor/symfony/http-kernel/HttpKernel.php(81): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#28 /app/web/core/lib/Drupal/Core/StackMiddleware/Session.php(58): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#29 /app/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#30 /app/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#31 /app/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#32 /app/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(48): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#33 /app/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(51): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#34 /app/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#35 /app/web/core/lib/Drupal/Core/DrupalKernel.php(713): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#36 /app/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#37 {main}
The problem exist after upgrading the environment to PHP8+ version.