This is my solution for this:
Add this to execute a particular script:
add_action('acf/input/admin_footer', array($this, 'filter_results'));
public function acf_filter_products_selection() {
?>
<script type="text/javascript">
(function($) {
acf.add_action('ready', function( $el ){
acf.add_filter('select2_ajax_results', function( json, params, instance ){
//Do whatever you want with the json.results array that contains the
//results from the DB
return json;
});
});
})(jQuery);
</script>
<?php
}