In my case, when creating a menu item to display a category it throws the following error:

0
"Event onContentBeforeDisplay only accepts String results"

https://www.joomshaper.com/forum/question/28712

here is a stack trace

Call stack

Function Location

1 () JROOT/libraries/src/HTML/HTMLHelper.php:141
2 Joomla\CMS\HTML\HTMLHelper::_() JROOT/templates/manufacturer/html/com_content/article/default.php:42
3 include() JROOT/libraries/src/MVC/View/HtmlView.php:415
4 Joomla\CMS\MVC\View\HtmlView->loadTemplate() JROOT/libraries/src/MVC/View/HtmlView.php:203
5 Joomla\CMS\MVC\View\HtmlView->display() JROOT/components/com_content/src/View/Article/HtmlView.php:244
6 Joomla\Component\Content\Site\View\Article\HtmlView->display() JROOT/libraries/src/MVC/Controller/BaseController.php:660
7 Joomla\CMS\MVC\Controller\BaseController->display() JROOT/components/com_content/src/Controller/DisplayController.php:121
8 Joomla\Component\Content\Site\Controller\DisplayController->display() JROOT/libraries/src/MVC/Controller/BaseController.php:693
9 Joomla\CMS\MVC\Controller\BaseController->execute() JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
10 Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch() JROOT/components/com_content/src/Dispatcher/Dispatcher.php:56
11 Joomla\Component\Content\Site\Dispatcher\Dispatcher->dispatch() JROOT/libraries/src/Component/ComponentHelper.php:361
12 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/SiteApplication.php:208
13 Joomla\CMS\Application\SiteApplication->dispatch() JROOT/libraries/src/Application/SiteApplication.php:249
14 Joomla\CMS\Application\SiteApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:293
15 Joomla\CMS\Application\CMSApplication->execute() JROOT/includes/app.php:61
16 require_once() JROOT/index.php:32