Thank you for creating the plugin, it is very helpful. Digging into this a bit, I believe the issue is in this code on lines 119 & 129:
if ( 'on' === $options['grid'] ) {
There are numerous threads about this being an issue when people move to PHP 7.4. Would it possible to get an updated version of the plugin that resolves this notice? It is filling up log files.
Thanks!