Trying to access array offset on value of type bool in layout-4.php on line 194

I have had a look at the debugging log on a website and this error keeps on occurring – “Trying to access array offset on value of type bool in /httpdocs/wp-content/plugins/nd-shortcodes/addons/templates/archive/layout/layout-4.php on line 194”. This seems to be related to a series of 520 errors when accessing the Dashboard. The site is running WP 5.7.1 and PHP 7.4.36. Can anybody shed any light on this?