By default, many Learndash-friendly themes chose a sidebar layout by default for course stages and lessons. We have made use of some CSS code native to the BuddyBoss theme that we use and implemented a full-width option by employing WP Bakery Page Builder. Out of the box, our learning site packages come set up to include Page Builder inside your stage/lesson page edit view. Using this we can inject a code that forces full-width for that particular page. Please see below for the implementation. Here is the code so you can copy-paste it for any page where you need a no-sidebar situation!

/* WORKBOOK PAGE SIDEBAR HIDE */
#secondary {display: none!important; }
#primary {width: 100%!important; }