@PabloL obviously we do not have visibility to all the details of your form and the rules, and at a high level would also recommend looking at the overall optimization of the form and intended outcome.  Optimization can be in the form of asking stakeholders “can we have fewer controls/fields and rules to get to the true outcomes we are looking for”.  Optimization in some cases will improve response times, not only for system response time, but also user response/completion ratio.

Understood.  In a normal project, I would be asking the users to come back with optimized requirements.  In this project, I was asked to create a prototype that would replace an existing collection of request forms (about 50 of them).  I wanted to see if I could combine all 50 separate forms into 1 form, for easier overall maintenance.  I thought of using Rules to decide which fields would show up.  This is for proof of concept only right now.

Side note - I also tried the method of using 2 SharePoint Online lists and 2 “data lookup” controls to implement this cascading dropdown menu.  It still results in a delay, of about 5 seconds.

If this delay cannot be resolved, I will implement instead a basic radio button control with all the 50 options at once.

@PabloL I can see the optimization in # of forms .  Great creative ideas in getting around this!

After several different strategies, including using data lookups into SharePoint Online & SQL tables, I still have not found a method that does not have a delay.

I am thinking that perhaps I should look into developing a form plugin for this feature.  I’m reviewing the documentation right now.  It does not yet make sense to me but perhaps soon I can find a web component that does the cascading dropdowns and convert it to a form plugin and that will solve my requirements.

Form plugins (nintex.com)

There are two ideas for this, go vote for idea

There is not currently a way to get distinct values in | Nintex Ideas. This idea was created in 2020. It’s been an issue for a while. It needs to be fixed. Functionality for distinct exists in other products, but not in NAC. This has 14 votes. 

The issue is in fact the distinct feature is not available on lookup controls like it is through Nintex Forms for Office 365.

My idea was created back in November 2022. However, I was told low votes so it wasn’t being planned. I hope this changes because it only allows for a list of data and if you want to cascade you have to have options for users to pick through multiple choice fields. My idea only received 3 votes. 
NAC Start Event Form - Cascading Dropdowns (Data | Nintex Ideas