magento 2.4.6 snippet [$block, ‘toHtml’] not working

Can anybody explain this magento 2.4.6 statement from core file ?

$alertGrid = $this->_appState->emulateAreaCode(
        Area::AREA_FRONTEND,
        [$block, 'toHtml']
    );

In the above code snippet there is an error. But I don’t know how to debug this snippet.what is this statement means[$block, 'toHtml']. I am trying to send some product alert information over email to the customer but the execution process is not reaching to the template file. as per my debug $block is a php class with one protected variable and that variable value is “phtml template file“. I don’t know how to explain this issue but someone of you might understand what exactly I am looking for.