The LifterLMS Courses (or Memberships) page, as defined in your LifterLMS settings, cannot be selected as the WordPress “Front Page”
You can work around this issue by using shortcodes on a custom page created for your Front Page.
- Create a new page which contain the shortcode “[lifterlms_courses]” (or [lifterlms_memberships] as the content of the page
- Set this page as the WordPress Front Page under WordPress Settings -> Reading Settings
Your Front Page will now display your courses list.