OK, use the Code Snippets plugin to add this snippet to your site:
function lh_page_hero_gravatar() {
ob_start();
global $post;
$author_id = $post->post_author;
?>
<div class="page-hero-gravatar">
<?php echo get_avatar( $author_id ); ?>
</div>
<?php
return ob_get_clean();
}
add_shortcode( 'page_hero_gravatar', 'lh_page_hero_gravatar' );
OR Alternatively rebuild your Header Elenments using the Block Element:
https://docs.generatepress.com/article/block-element-page-hero/