JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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The Unique ID widget can be hidden only, but there is another widget that will be shown on the form, here is the link to the widget: https://widgets.jotform.com/widget/random_value_generator
This will generate a value that you can also customize.
Also, the Unique ID widget can be shown, but only on emails and Thank You page, to show the field's value on your Thank You page you will need to include it from the Form Fields drop down:
Hope this helps.