How do I access the checkbox field column value as a PHP array?
MultiOptionsFieldData extends PHP's ArrayObject class.

You could get the values from it by casting it to an array like so:

$results = (array)$mofd;


That would give you an array of OptionData classes.  If you really didn't want to loop through them, you could do something like:

$func = static function($ofd) {
    return $ofd-&gt;value;
};

$results = array_map($func, (array)$mofd);