No clue if the latest Responsive Forms can solve this for you, but it can be solved in Classic Forms by way of Custom JavaScript. Which form type are you using now?

I’m using the latest responsive designer. 

Unfortunately then I do not believe that you will be able to accomplish what it is you’re trying to do unless someone like @Garrett has a trick up their sleeve for producing dynamic dropdown lists.

Perhaps unintuitively the latest and greatest Nintex stuff isn’t designed with deep customization in mind, but is targeted more at providing a code-free solution to getting some sort of automation / data-collection that works just good enough.

If you want to do any sort of real customization of the form you need to be able to run custom javascript, and the only way to do that in the latest New Responsive Forms in SharePoint Online (or even just the (now older) Responsive Forms in SharePoint On Prem) is to use fairly sketchy methods that are not technically “intended” and therefore are unreliable in the event that Nintex patches them out.

Hi @anderj39, @MegaJerk 

You need to use Lookup List for for dynamic dropdowns.

Are the choices presented as Cascading dropdowns? Is there an order to which item is selected first?

If you want dynamic list - select choice A, list changes, select choice B, list changes again.
This is not possible as there is no way to remove or add or rename list items.

@anderj39 perhaps you could provide the full details of the values. 

If you really wanted something like that and there is only four or less variation.
I don’t really recommend it but I would create 4 Groups. Each group caters to one variation.
Each group has its own dropdown list with the items for that particular variation.
Use form rule(s) to determine which single group to show (made visible) and the other groups must hidden.
Use a form rule to copy/save the selected item value to a text control (which is connected to SPO column)

The main reason for not recommending this method is that if the variation increases (it increases exponentially), you have a hard time maintaining all the dropdown list

Thank you for the replies and suggestions!!

The Filed question only pertains to 2 of the Plan options.  There’s actually a 4th question also in play that only pertains to 1 of the plan options. 

Not currently using a lookup because of the variances. And to your point, those lists could likely grow and be a nightmare to maintain. And based on all the variances involved, there would be about 6 groups to maintain.

Didn’t want to use Classic as I love the easy and clean look of the responsive designer. The Responsive form allows me to get about 95% of what I need. Was hoping there would be loopholes to use some simple JS or formula based conditions.

While waiting for responses, I went ahead and created Validation rules to capture everything. That’ll at least prevent them from submitting. Sounds like that might be the best I can do.