As you build out a new course or program, you may want to hide it from the Marketplace until it's 100% ready.
This is easy to do.
In Step 4 of your course builder, open up the Page Builder by clicking the green button.
Click on the Marketplace page to open it
Edit the block that holds your course
Open the Data dropdown menu
Navigate to "Select Courses to Display". Click to remove the course that you don't want shown in the Marketplace
Once this is done, your Course won't appear on the Marketplace any longer.
Keep in mind though that if a student already has access to the Course in question, they will still be able to log into it.
If you want to add the course back in, in the future, simply scroll through the list of your courses and select the courses that you want to appear.