Edit Post Types via API / Programmatically?

Thanks Peter.

So I've created a code snippet and managed to pull with API 'mb-post-type'. But I don't get back the fields from 'mb-post-type' (when make the request to the post type and Id, like: /wp/v2/mb-post-type/112). The only thing I get are 'slug', 'status', 'type' etc. How can I get back the fields?

For example I want to be able to see and update the values for these under 'Advanced': https://loom.com/i/73eb07b1ec7c44b293f16d9a73715b2e

This is my code snippet:

// Enable REST API for mb-post-type only
function enable_rest_api_for_metabox_post_type($args, $post_type) {
    if ($post_type === 'mb-post-type') {
        $args['show_in_rest'] = true;
    }
    return $args;
}
add_filter('register_post_type_args', 'enable_rest_api_for_metabox_post_type', 10, 2);

// Add all meta keys to REST API for mb-post-type
function add_all_meta_to_rest_api() {
    register_rest_field(
        'mb-post-type',
        'all_meta',
        array(
            'get_callback' => function($post) {
                return get_post_meta($post['id']);
            }
        )
    );
}
add_action('rest_api_init', 'add_all_meta_to_rest_api');

I've done a lot of back and forth with Claude to try and expose everything - but I can't figure out how to see the fields