Remove close action from overlay

Hi,

I would like to remove close action from overlay so user would be able to close the box only with [boxzilla-close] button.

I found this filter to disable box closure:

add_filter( 'boxzilla_box_options', function( $opts, $box ) {
$opts['closable'] = false;
return $opts;
}, 10, 2 );

but it disables closure with [boxzilla-close] as well.

Is there any other function/filter to remove close action from overlay only?
Alternatively – could I use above code and add something to [boxzilla-close] to make it work?

Any help would be much appreciated.