WordPress Twenty Twenty theme custimizations, via custom plugin (e.g., mod date in post meta)

wp_2020_custom.php

<?php 
/**
 * Adds modified date to displayed post meta.
 *
 * Uses action in theme's /inc/template-tags.php file.
 * Param values passed by the action hook.
 * @param int    $post_id  The ID of the post.
 * @param array  $post_meta An array of post meta information.
 * @param string $location The location where the meta is shown.
 */
function my_mod_meta( $post_id, $post_meta, $location ) {
    // If post was modified since publication.
    if ( get_the_modified_time( 'U', $post_id ) > get_the_time( 'U', $post_id ) ) {

    $has_meta = true;
    ?> // Add list item to post meta with mod date.
<li class="post-date meta-wrapper">
    <?php _e( 'Update:&nbsp;', 'twentytwenty' ); ?> <time class="meta-text"><?php the_modified_time( get_option( 'date_format' ) ); ?></time>
</li>
    <?php
    }
}
add_action( 'twentytwenty_end_of_post_meta_list', 'my_mod_meta', 10, 3 );