The ACF class names changed and so you need to adjust that. This one works for me:
add_action('acf/input/admin_head', 'my_acf_admin_head_flex');
function my_acf_admin_head_flex() {
?>
<script type="text/javascript">
(function($) {
acf.add_action('ready', function(){
$('body').on('click', '.acf-fc-layout-controlls .acf-icon.-minus.small', function( e ){
return confirm("Tem certeza que irá deletar este item?");
});
});
})(jQuery);
</script>
<?php
}
