Add new tag to lessons/topics/quizzes inside LeanrDash course table which are updated within 30 days

functions.php

<?php
add_action( 'learndash-lesson-row-title-after', 'learndash_add_tag_to_new_lessons', 10, 3);

function learndash_add_tag_to_new_lessons( $lesson_id, $course_id, $user_id ) {
	$lesson = get_post( $lesson_id );

	if ( strtotime( $lesson->post_modified ) > strtotime( '-30 days' ) ) {
		echo "<span class='ld-content-new-tag'>" . __( "(New)", 'sfwd-lms' ) . "</span>";
	}
}

add_action( 'learndash-topic-row-title-after', 'learndash_add_tag_to_new_topics', 10, 3);

function learndash_add_tag_to_new_topics( $topic_id, $course_id, $user_id ) {
	$topic = get_post( $topic_id );

	if ( strtotime( $topic->post_modified ) > strtotime( '-30 days' ) ) {
		echo "<span class='ld-content-new-tag'>" . __( "(New)", 'sfwd-lms' ) . "</span>";
	}
}

add_action( 'learndash-quiz-row-title-after', 'learndash_add_tag_to_new_quizzes', 10, 3);

function learndash_add_tag_to_new_quizzes( $quiz_id, $course_id, $user_id ) {
	$quiz = get_post( $quiz_id );

	if ( strtotime( $quiz->post_modified ) > strtotime( '-30 days' ) ) {
		echo "<span class='ld-content-new-tag'>" . __( "(New)", 'sfwd-lms' ) . "</span>";
	}
}

Place this snippet in your theme's functions.php file and a New tag will be displayed next to lessons/topcis/quizzes inside the LeanrDash course content table on the course page.
Please note that a CSS class is added to all the new tags .ld-content-new-tag so that you can easily design the look and feel by adding CSS rules in your theme's custom CSS