Joomla 4.2.4
PHP 8.0
I migrated my site to J4. I first installed the Asteroid framework and the latest version of the Advokat template.
After update, I get this error on the backend only on the controlpanel:
Joomla\CMS\Application\AdministratorApplication::isSite()

The other pages in the backend work as normally.

Although, the frontend also gives the same error.

I had no extensions of third parties that could give problems after update so I don't know where to find the problem and how to solve it.

Did you migrate from Warp-Framework?

And please activate the call stack, to find incompatible extensions:

forum.joomla.de/thread/6467-fehler-finde...ug-modus-call-stack/

Hello,
it seems to be a Joomla problem with PHP 8 and J4 and the new cache system in Joomla 4
Please disbale all cache options in Joomla and delete the cache too

Yes, but I did that update before migrating to J4 and that was all fine.I disabled a plugin of JCE quick icon and the backend is ok now.The frontend is still not working though. These are the errors that I get.

() JROOT/administrator/components/com_jce/classes/model.php:11
2 require_once() JROOT/administrator/components/com_jce/models/model.php:13
3 require_once() JROOT/administrator/components/com_jce/helpers/browser.php:17
4 WFBrowserHelper::getBrowserLink() JROOT/administrator/components/com_jce/helpers/browser.php:26
5 WFBrowserHelper::getMediaFieldLink() JROOT/plugins/system/jce/fields/mediajce.php:65
6 JFormFieldMediaJce->getLayoutData() JROOT/libraries/src/Form/Field/MediaField.php:246
7 Joomla\CMS\Form\Field\MediaField->getInput() JROOT/libraries/src/Form/FormField.php:1029
8 Joomla\CMS\Form\FormField->renderField() JROOT/layouts/joomla/content/options_default.php:42
9 include() JROOT/libraries/src/Layout/FileLayout.php:128
10 Joomla\CMS\Layout\FileLayout->render() JROOT/libraries/src/Layout/LayoutHelper.php:76
11 Joomla\CMS\Layout\LayoutHelper::render() JROOT/administrator/components/com_config/tmpl/application/default_site.php:20
12 include() JROOT/libraries/src/MVC/View/HtmlView.php:410
13 Joomla\CMS\MVC\View\HtmlView->loadTemplate() JROOT/administrator/components/com_config/tmpl/application/default.php:43
14 include() JROOT/libraries/src/MVC/View/HtmlView.php:410
15 Joomla\CMS\MVC\View\HtmlView->loadTemplate() JROOT/libraries/src/MVC/View/HtmlView.php:203
16 Joomla\CMS\MVC\View\HtmlView->display() JROOT/administrator/components/com_config/src/View/Application/HtmlView.php:100
17 Joomla\Component\Config\Administrator\View\Application\HtmlView->display() JROOT/libraries/src/MVC/Controller/BaseController.php:639
18 Joomla\CMS\MVC\Controller\BaseController->display() JROOT/administrator/components/com_config/src/Controller/DisplayController.php:63
19 Joomla\Component\Config\Administrator\Controller\DisplayController->display() JROOT/libraries/src/MVC/Controller/BaseController.php:672
20 Joomla\CMS\MVC\Controller\BaseController->execute() JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
21 Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch() JROOT/libraries/src/Component/ComponentHelper.php:355
22 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/AdministratorApplication.php:143
23 Joomla\CMS\Application\AdministratorApplication->dispatch() JROOT/libraries/src/Application/AdministratorApplication.php:186
24 Joomla\CMS\Application\AdministratorApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:294
25 Joomla\CMS\Application\CMSApplication->execute() JROOT/administrator/includes/app.php:61
26 require_once() JROOT/administrator/index.php:32

Update the jce Editor.

I did and that solved partially my problem.
Apparantly, there is still a problem with the framework. I get this code on the frontend:

TypeError:
Astroid\Framework::getDocument(): Return value must be of type Astroid\Document, null returned

at /home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/astroid/framework/library/astroid/Framework.php:85
at Astroid\Framework::getDocument()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/templates/tp_advocat/error.php:20)
at require('/home/medi3359/domains/cindesign.be/public_html/spiegelogen/templates/tp_advocat/error.php')
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Document/HtmlDocument.php:736)
at Joomla\CMS\Document\HtmlDocument->_loadTemplate()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Document/HtmlDocument.php:791)
at Joomla\CMS\Document\HtmlDocument->_fetchTemplate()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Document/HtmlDocument.php:608)
at Joomla\CMS\Document\HtmlDocument->parse()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Document/HtmlDocument.php:626)
at Joomla\CMS\Document\HtmlDocument->render()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Document/ErrorDocument.php:139)
at Joomla\CMS\Document\ErrorDocument->render()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Error/Renderer/HtmlRenderer.php:78)
at Joomla\CMS\Error\Renderer\HtmlRenderer->render()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Exception/ExceptionHandler.php:121)
at Joomla\CMS\Exception\ExceptionHandler::render()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Exception/ExceptionHandler.php:72)
at Joomla\CMS\Exception\ExceptionHandler::handleException()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/libraries/src/Application/CMSApplication.php:323)
at Joomla\CMS\Application\CMSApplication->execute()
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/includes/app.php:61)
at require_once('/home/medi3359/domains/cindesign.be/public_html/spiegelogen/includes/app.php')
(/home/medi3359/domains/cindesign.be/public_html/spiegelogen/index.php:32)