When using the Tesseract theme, sidebars will work as long as you have sidebars displaying in the Tesseract Layout options under the Customizer. If you select a full-width layout, you’ll want to add the following snippet to your functions.php file. This will ensure that LifterLMS Course and Lesson sidebars display regardless of the site-wide layout options defined by the Tesseract theme.
As is, this adds right-side sidebars to courses and lessons. If you comment out line 16 and uncomment line 15, left-side sidebars will be enabled. You could also pass “fullwidth”, as in line 20, this would make the posts fullwidth.