Hi @Underdog 

You have an existing form on your SharePoint site and you would like to create another Form for that site. Did I understand your requirements correctly?

You need to enable Content Type on the List. Go to "Advanced settings" of your list and then turn on content types option. 

Each Nintex Form is tied to a content type. Without adding another content type, you can only have 1 Nintex Form per SP site. So, if your list has 5 content type, you may add up to 5 forms to the list

Cheers

Hi Garrett,

Could you send me a screenshot of the "Advanced Settings" location?

Thanks!

I am using the SP Modern (not Classic) style.

Go to List Settings. There is a link to Advance Settings.

I believe that you are using the SP Classic style.

Cheers

This is one I'm looking at ..

Excellent.  So do I change "Allow management of content types."

Yes. Allow Management. Click OK

Then you need to create a new content type for your list.

FYI, Item is the default SP List

Ok.  So far so good.  I don't see "Item" though.  Thoughts?

Once you done the previous steps.

You will notice that you have 2 content type. 
You can set whether both are Visible on the New Button and which is the Default.
You can set whether a column is visible to both List content  

You can't add Item. Item is the default content type. Add Issues.
Sorry about that. I highlight items but I forgot to explain it

When you return to your List.

Click Nintex Forms. Nintex Forms will prompt which Content Type to build your form.

Added.

So, as directed .. looking good.  The first screenshot below looks right.  "Item" is the default, and can remain the default.  The next screenshot shows "Item" in the "Used in" column.  Should I see both "Item" & "Issue" in this column?  (As a note, the reason I'd like a second Form is to modify my first form using the second Form as a development Form.  Once I get the new Form where I want it, then I'll modify the first Form).

So, if desired, how would I make the "Used in" column both "Item/Issue"?

Click the content type. then add the columns which you want
To add "Used in" column to both "Item/Issue", (which is already in Item), click Issue.  

Click Add from existing site.

Ok.  As I understand it, click by the yellow arrow ..

Then comes this:

Hi @Underdog 

Did you manage to create your 2nd form?

Which choice is better for customization?

That's an entirely different line of questions @Underdog  

You should ask that as a new question. There are pros and cons to both types of form. 

Unfortunately I don't use both of those types. 

FYI, My organization has standardize on New Responsive Form (we are on Nintex O365 and moving towards NWC). 

Many of the users with technical background prefer the Classic form. 
They are able to extend the form capability through the usage of JavaScript.

Nintex Mobile is unable to use JavaScript.

Business users (those Excel Macros whiz) tend to prefer the Responsive / NewResponsive form.

They prefer the responsive nature to device viewscreen (desktop or mobile).

The Responsive form has a more modern UI feel and is mobile ready.

Ask the community and see what they say