I was able to use the Post Excerpt block along with the “get_the_excerpt” filter to get this working. Something like this:
add_filter( 'get_the_excerpt', 'my_the_excerpt', 10, 2 );
function my_the_excerpt( $excerpt, $post ) {
if ( strpos( $post->post_content, '<!--more-->' ) ) {
return get_the_content();
}
return $excerpt;
}