error Class "Text" not found

There is suddenly an error message in the backend homepage dashboard: An error has occurred. 0 Class "Text" not found. (See screenshot)
The whole thing happens with Firefox and Edge and on 2 different websites.

What I did last: an update of "JEM" 2.3.17->4.0.0 (without problems).
I already sent the problem to the joomla-forum. The joomla-people suspect a Bug in JEM.

Everything else still seems to work but I'm a bit nervous now.

The DEBUG in backend shows:
Call stack
# Function Location
1 () JROOT/plugins/quickicon/jemquickicon/jemquickicon.php:37
2 plgQuickiconJEMquickicon->onGetIcons() JROOT/libraries/src/Plugin/CMSPlugin.php:284
3 Joomla\CMS\Plugin\CMSPlugin->Joomla\CMS\Plugin\{closure}() JROOT/libraries/vendor/joomla/event/src/Dispatcher.php:486
4 Joomla\Event\Dispatcher->dispatch() JROOT/libraries/src/Application/EventAware.php:111
5 Joomla\CMS\Application\WebApplication->triggerEvent() JROOT/administrator/modules/mod_quickicon/src/Helper/QuickIconHelper.php:386
6 Joomla\Module\Quickicon\Administrator\Helper\QuickIconHelper->getButtons() JROOT/administrator/modules/mod_quickicon/src/Dispatcher/Dispatcher.php:38
7 Joomla\Module\Quickicon\Administrator\Dispatcher\Dispatcher->getLayoutData() JROOT/libraries/src/Dispatcher/AbstractModuleDispatcher.php:63
8 Joomla\CMS\Dispatcher\AbstractModuleDispatcher->dispatch() JROOT/libraries/src/Helper/ModuleHelper.php:281
9 Joomla\CMS\Helper\ModuleHelper::renderRawModule() JROOT/libraries/src/Helper/ModuleHelper.php:161
10 Joomla\CMS\Helper\ModuleHelper::renderModule() JROOT/administrator/components/com_cpanel/tmpl/cpanel/default.php:57
11 include() JROOT/libraries/src/MVC/View/HtmlView.php:410
12 Joomla\CMS\MVC\View\HtmlView->loadTemplate() JROOT/libraries/src/MVC/View/HtmlView.php:203
13 Joomla\CMS\MVC\View\HtmlView->display() JROOT/administrator/components/com_cpanel/src/View/Cpanel/HtmlView.php:158
14 Joomla\Component\Cpanel\Administrator\View\Cpanel\HtmlView->display() JROOT/libraries/src/MVC/Controller/BaseController.php:645
15 Joomla\CMS\MVC\Controller\BaseController->display() JROOT/administrator/components/com_cpanel/src/Controller/DisplayController.php:56
16 Joomla\Component\Cpanel\Administrator\Controller\DisplayController->display() JROOT/libraries/src/MVC/Controller/BaseController.php:678
17 Joomla\CMS\MVC\Controller\BaseController->execute() JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
18 Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch() JROOT/libraries/src/Component/ComponentHelper.php:361
19 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/AdministratorApplication.php:143
20 Joomla\CMS\Application\AdministratorApplication->dispatch() JROOT/libraries/src/Application/AdministratorApplication.php:186
21 Joomla\CMS\Application\AdministratorApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:293
22 Joomla\CMS\Application\CMSApplication->execute() JROOT/administrator/includes/app.php:61
23 require_once() JROOT/administrator/index.php:32

I can't reproduce your issue. For me it seems, it has to do with the JEM quickicon plugin.
In my case I don't see no JEM icon (it should be visible?) What does the JEM quickicon?
Do you have JEM quickicon enabled? Is the problem solved when you disable JEM Quickicon?

Found something in the debug-list
1 () JROOT/plugins/quickicon/jemquickicon/jemquickicon.php:37
In this line a J is missing in "JText"
If I enter it, it's ok.
2. Try : when I disable the Admin module "3RD party" containing the JEM quickbutton it also works. (I m in a train so sorry for typos)

Hi Sepp

Thanks for reportin this error.

Adding "J" works, butt it is from Joomla 3 and deprecated (old)

Instead leave in line 37 and add a line unter line 12:

Change
to

That should fix it the correct way for Joomla 4.

Thank you. This works.
I saw this line in other PHPs but didn't understand.
What does "use Joomla\CMS\Language\Text;" mean ?
best regards

@sepp25 This is the class that contains the Joomla functions for dealing with and manipulating strings.
Thanks for reporting it.