You are notified there is a new topic to be approved, you click on the notification and will be taken to the mcp where you will disapprove it, getting back to the mcp page you will see the errors.

The screenshot shows different lines due to my debugging in that file.

//[phpBB Debug] PHP Notice: in file [ROOT]/mcp.php on line 91: Trying to access array offset on value of type bool

//[phpBB Debug] PHP Notice: in file [ROOT]/mcp.php on line 92: Trying to access array offset on value of type bool