How to stop the slide from advancing until all the click boxes have been selected

Some crucial information is missing from your question: which version do you use (exact number please)?

You need to create an advanced action for each click box. I cannot give exact details since I am unaware of the version, and advanced actions dialog box has changed in CP2017. Look at: Advanced Actions Dialog box in Captivate 2017 - Captivate blog

To start with you need a user variable per click box, will label them v_one, v_two......; v_last. They are Booleans, starting with a default value of 0, which will be toggled to 1 when the click box has been clicked.

The advanced action has two parts:

Part 1: has always to be executed, with your commands (of showing feedback, probably closing other feedback) and changing its user variable. For click box 1 this could be:

       Hide Gr_Feedback

       Show Feedback1

       Assign v_one with 1

Part 2: will check all values of the user variables and when they are all set to 1, will navigate to the next slide:

    IF v_one is equal to 1    AND

        v_two is equal to 1   AND

        .....

        v_last is equal to 1

   Go to Next Slide

  ELSE

    Continue

Create a duplicate of this action for each click box, you only have to change the Feedback name and user name in the duplicates.

All click boxes need to have their pausing point at the same moment.