permission_callback has no effect

WP version is 5.5.3

I have 3 API routes set in a plugin that is used in an admin dashboard page. One route is meant to be used publicly.

I have two very curious issues happening:

1. My 3 admin-centric routes do not specify permission_callback. I should be getting notices but I do not when the docs and WP core functions say it will throw a doing_it_wrong error.
2. My 4th public route does have 'permission_callback' = '__return_true' set. I receive a rest_not_logged_in error code.

class My_Plugin
{
    public function __construct()
    {
        add_action( 'rest_api_init', [ $this, 'register_routes' ] );
    }
    
    public function register_routes(): void
    {
        register_rest_route('my-api-route', '/uri', [
            'methods' = WP_REST_Server::READABLE,
            'callback' = [$this, 'api_get_available_stuff'],
        ]);

        register_rest_route('my-api-route', /uri/(?Pparam[a-zA-Z0-9-]+), [
            'methods' = WP_REST_Server::READABLE,
            'callback' = [$this, 'api_get_specific_stuff'],
        ]);

        register_rest_route('my-api-route', /uri/(?Pparam[0-9-]+), [
            'methods' = WP_REST_Server::EDITABLE,
            'callback' = [$this, 'api_update_specific_stuff'],
        ]);

        register_rest_route('my-api-route', /uri/(?Pparam[a-zA-Z0-9-]+)/load-more, [
            'methods' = WP_REST_Server::READABLE,
            'callback' = [$this, 'api_load_more_stuff'],
            'permission_callback' = '__return_true',
        ]);
    }
}

// header approach
$.ajax({
  url: '/wp-json/my-api-route/uri/param/load-more',
  method: 'GET',
  headers: {
    'X-WP-Nonce': '?php echo wp_create_nonce('wp_rest'); ?'
  },
  data: {
    'max_items': 5,
    'offset': 5 * current_count,
  },
})

// _wpnonce approach
$.ajax({
  url: '/wp-json/my-api-route/uri/param/load-more',
  method: 'GET',
  data: {
    '_wpnonce': '?php echo wp_create_nonce('wp_rest'); ?',
    'max_items': 5,
    'offset': 5 * current_count,
  },
})

My only conclusion could be that, despite seeing Version 5.5.3 in the bottom corner of WP Admin, I might not actually be on 5.5.3.