Source: https://www.elegantthemes.com/blog/divi-resources/how-to-add-the-last-updated-date-to-divis-blog-post-meta-data

Show the “last updated” date.

Paste the following code snippet into your child theme’s functions.php file:

function et_last_modified_date_blog( $the_date ) {
    if ( 'post' === get_post_type() && !is_admin() ) {
        $the_time      = get_post_time( 'His' );
        $the_modified  = get_post_modified_time( 'His' );
        $last_modified =  sprintf( __( 'Last updated %s', 'Divi' ), esc_html( get_post_modified_time( 'M j, Y' ) ) );
        $date          = $the_modified !== $the_time ? $last_modified : get_post_time( 'M j, Y' );
 
        return $date;
    }
 
    return $the_date;
}
add_filter( 'get_the_date', 'et_last_modified_date_blog' );
add_filter( 'get_the_time', 'et_last_modified_date_blog' );Code language: PHP (php)

Show the publish date and the last updated

function et_last_modified_date_blog( $the_date ) {
    if ( 'post' === get_post_type() && !is_admin() ) {
        $the_time      = get_post_time( 'His' );
        $the_modified  = get_post_modified_time( 'His' );
        $last_modified =  sprintf( __( 'Last updated %s', 'Divi' ), esc_html( get_post_modified_time( 'M j, Y' ) ) );
        $date          = $the_modified !== $the_time ? $last_modified : get_post_time( 'M j, Y' );
 
        return $date;
    }
 
    return $the_date;
}
add_filter( 'get_the_date', 'et_last_modified_date_blog' );
add_filter( 'get_the_time', 'et_last_modified_date_blog' );Code language: PHP (php)