I can’t say for certain because you haven’t posted any code, but the error message makes it look like you still have the wrong namespace for app/controllers/App.php. The namespace for your controllers should be App\Controllers\[whatever the controller is], but the error here says that it’s just looking for Controllers\App instead of App\Controllers\App.
If you’re struggling with namespace, you may find this post I wrote attempting to explain how they work helpful: Controller namespace issue, different behavior on localhost and development server