How to display the Unique ID widget on my form?

Is there any way to show Unique ID? The preferences in show/hide field does not seem to work.

You can't show or display this widget on your form (from your user's perspective) because this widget gets triggered only after form submission. This would mean that the moment your form loads up, the widget doesn't have any unique value generated yet so there's nothing to display.

What you can do is place the Unique ID on your Autoresponder Email template or on your Thank You page.

Related guides:

Setting-Up-an-Autoresponder-Email

Setting-Up-the-Thank-You-Page

How-to-Edit-the-Email-Template-for-Notifications-and-Autoresponders