Enable the Featured Image on Learndash Topics/Lessons page

<?php
/**
 * LearnDash LD30 focus mode.
 *
 * @since 3.0.0
 *
 * @package LearnDash\Templates\LD30
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

if ( have_posts() ) :
    while ( have_posts() ) :
        the_post();

        $cuser     = wp_get_current_user();
        $course_id = learndash_get_course_id();
        $user_id   = ( is_user_logged_in() ? $cuser->ID : false );

        /**
         * Fires before the header in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-header-before', $course_id, $user_id );

        learndash_get_template_part(
            'focus/header.php',
            array(
                'course_id' => $course_id,
                'user_id'   => $user_id,
                'context'   => 'focus',
            ),
            true
        );

        /**
         * Fires before the sidebar in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-sidebar-before', $course_id, $user_id );

        learndash_get_template_part(
            'focus/sidebar.php',
            array(
                'course_id' => $course_id,
                'user_id'   => $user_id,
                'context'   => 'focus',
            ),
            true
        ); ?>

    <div class="ld-focus-main">

        <?php
        /**
         * Fires before the masthead in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-masthead-before', $course_id, $user_id );

        learndash_get_template_part(
            'focus/masthead.php',
            array(
                'course_id' => $course_id,
                'user_id'   => $user_id,
                'context'   => 'focus',
            ),
            true
        );

        /**
         * Fires after the masthead in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-masthead-after', $course_id, $user_id );
        ?>

        <div class="ld-focus-content">

            <?php
            /**
             * Fires before the title in the focus template.
             *
             * @since 3.0.0
             *
             * @param int $course_id Course ID.
             * @param int $user_id   User ID.
             */
            do_action( 'learndash-focus-content-title-before', $course_id, $user_id );
            ?>

            <h1>
                <?php
                    add_theme_support( 'post-thumbnails' );
                    the_post_thumbnail();
                    the_title();
                ?>
            </h1>

            <?php
            /**
             * Fires before the content in the focus template.
             *
             * @since 3.0.0
             *
             * @param int $course_id Course ID.
             * @param int $user_id   User ID.
             */
            do_action( 'learndash-focus-content-content-before', $course_id, $user_id );
            ?>

            <?php the_content(); ?>

            <?php
            /**
             * Fires after the content in the focus template.
             *
             * @since 3.0.0
             *
             * @param int $course_id Course ID.
             * @param int $user_id   User ID.
             */
            do_action( 'learndash-focus-content-content-after', $course_id, $user_id );
            ?>

            <?php
                wp_link_pages(
                    array(
                        'before' => '<div class="page-links">' . esc_html__( 'Pages:', 'learndash' ),
                        'after'  => '</div>',
                    )
                );
            ?>

            <?php
            /**
             * Filters whether to show existing comments when comments are not enabled.
             *
             * @since 3.4.2
             *
             * @param boolean $show_existing_comments Whether to show existing comments.
             */
            if ( comments_open() || ( apply_filters( 'learndash_focus_mode_show_existing_comments', false ) ) ) {
                /**
                 * Filters whether to load comments in focus mode or not.
                 *
                 * @since 3.1.4
                 *
                 * @param boolean $load_focus_comments Whether to show comments in focus mode or not.
                 */
                if ( apply_filters( 'learndash_focus_mode_can_view_comments', is_user_logged_in() ) ) {
                    learndash_get_template_part(
                        'focus/comments.php',
                        array(
                            'course_id' => $course_id,
                            'user_id'   => $user_id,
                            'context'   => 'focus',
                        ),
                        true
                    );
                }
            }
            ?>

            <?php
            /**
             * Fires at the focus mode content end.
             *
             * @since 3.1.4
             *
             * @param int $course_id Course ID.
             * @param int $user_id   User ID.
             */
            do_action( 'learndash-focus-content-end', $course_id, $user_id );
            ?>
        </div> <!--/.ld-focus-content-->

    </div> <!--/.ld-focus-main-->

        <?php
        /**
         * Fires before the footer in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-content-footer-before', $course_id, $user_id );

        learndash_get_template_part(
            'focus/footer.php',
            array(
                'course_id' => $course_id,
                'user_id'   => $user_id,
                'context'   => 'focus',
            ),
            true
        );

        /**
         * Fires after the footer in the focus template.
         *
         * @since 3.0.0
         *
         * @param int $course_id Course ID.
         * @param int $user_id   User ID.
         */
        do_action( 'learndash-focus-content-footer-after', $course_id, $user_id );

    endwhile;
else :

    learndash_get_template_part(
        'modules/alert.php',
        array(
            'type'    => 'warning',
            'icon'    => 'alert',
            'message' => esc_html__( 'No content found at this address', 'learndash' ),
        ),
        true
    );

endif; ?>