The most direct way to prevent the learner from clicking on the Next button (and passing the slide) is to disable the Next button until everything on the slide has been clicked/selected/viewed.
To disable the Next button, add a trigger that is configured to "Change the state of the Next button to disabled when the timeline on this slide starts." Then add a second trigger that is configured to "Change the state of the Next button to normal when..." And then add the condition at which you want the learner to be able to advance.