Hi there,
Yoast will only appear on Publicly Queryable Post types, which GP Elements are not.
You can make them so with snippet.
add_action('register_post_type_args', function ($args, $postType) {
if ($postType !== 'gp_elements'){
return $args;
}
$args['public'] = true;
return $args;
}, 99, 2);
Then you will be able to enable Elements post type in the Yoast Settings.
Not sure what repercussions could be for making them public, as they may show up in feeds….