Custom PHP8 attribute such as ObservedBy not working as expected

Howdy all, I've got a Laravel 11 project. My PHP Version is 8.3. Using Homestead on Windows.

I can't get any PHP8 attributes to work as expected. For example:

#[ObservedBy([UserObserver::class])]
class User extends Authenticatable
{
    //
}

My UserObserver::class definitely exists. When I create a UserFactory, the observer is never called.

However, if I register the Observer manually via AppServiceProvider, it works perfectly i.e.:

public function boot(): void
{
    User::observe(UserObserver::class);
}

I was under the impression that as of PHP8.0, these attributes should work. Is there something I may be missing?