Custom Blog meta with author name outside of WordPress loop

custom-meta.php

if ( ! function_exists( 'atmosphere_posted_on' ) ) :
  /**
   * Prints HTML with meta information for the current post-date/time and author.
   */
  function atmosphere_posted_on() {
    global $post;
    $author_id = $post->post_author;
    $author = get_the_author_meta('display_name', $author_id);
    $time_string = '<time class="entry-date published updated" datetime="%1$s">%2$s</time>';
    if ( get_the_time( 'U' ) !== get_the_modified_time( 'U' ) ) {
      $time_string = '<time class="entry-date published" datetime="%1$s">%2$s</time><time class="updated" datetime="%3$s">%4$s</time>';
    }
    $time_string = sprintf( $time_string,
      esc_attr( get_the_date( 'c' ) ),
      esc_html( get_the_date() ),
      esc_attr( get_the_modified_date( 'c' ) ),
      esc_html( get_the_modified_date() )
    );
    $posted_on = sprintf(
      /* translators: %s: post date. */
      esc_html_x( 'Posted on %s', 'post date', 'gutenbergtheme' ),
      '<a href="' . esc_url( get_permalink() ) . '" rel="bookmark">' . $time_string . '</a>'
    );
    $byline = sprintf(
      /* translators: %s: post author. */
      esc_html_x( 'by %s', 'post author', 'gutenbergtheme' ),
      '<span class="author vcard">' . esc_html( get_the_author_meta('display_name', $author_id) ) . '</span>'
    );
    echo '<span class="posted-on">' . $posted_on . '</span><span class="byline"> ' . $byline . '</span>'; // WPCS: XSS OK.
  }
endif;