Duplicate fields in JotForm version 4

I do not see this option in the 4.0 version, where do I find it?

Thanks for informing us. It appears that option has been removed temporarily. Please bear with us while we're improving the open beta version (V4).

With that in mind, options and features may come in and out while undergoing QAs and tests.

For your reference, this is how you're supposed to see the duplicate option in V4:

Check back V4 from time to time if you wish to use it to build forms. But if you need to duplicate fields, for now, I would suggest you use our current stable version (V3) by doing what is shown on the screenshot you sent us.