Just came across your activity. I applaud your use of boredom time.
What is missing from your marbleslides is any way for students to move the objects that control the motion of the marbles. Those need to be in cells that are outside the folder that you use to make the fixed items. Take a peek at one of the marbleslides made inhouse at Desmos (such as https://teacher.desmos.com/activitybuilder/custom/5c51fe3699178a0c1076f261/edit ). I (very clumsily) added such to one of yours at [Copy of] Marbleslides: Expert • Activity Builder by Desmos The Desmos team shows you how to do such more elegantly.
I look forward to revisiting your work once you have updated it.