Quizzing system variables, and AFAIK all system variables in the new version are read only. Exception are a couple of minor toggle variables (lock TOC, hide/show playbar/TOC). You may be able to manipulate them using JS but I have not yet tested it out because I continue to use the more complete version 11.5.5 for my professional jobs. I have written tons of blogs about Quizzes for previous versions.
What I propose in your use case is:
- Add a score to the button (or other object) that needs to be clicked by any learner. You do so by using the interaction button and scrolling down to the bottom part where you can activate Reporting and edit the score. I propose a big score of 50points. It will be the only 'scored object'.
- For a weird reason setting up the passing score of a course has been taken out of the Quiz Preferences, don't shoot the pianist, but the composer. Hence a rather quirky workflow: add the score slide to the project.
- Click the Interaction button for that score slide and you'll see the setup for the passing score. You can require 100% (most LMSs work better with percentages than points).
- For some settings you may need to complete in Quiz Preferences.
- Hide the score slide.
I know, should test this workflow and write it out, but so many 'experts' proclaim to know everything about the new Captivate but ignore or never tried out workarounds like this one. Such a claim is ridiculous, because you cannot recreate a database of knowledge which has grown during two decades for the older versions in a couple of months. And a majority of questions reappear about quizzes.