REST API – filters not working inside plugin class

This is a problem:

public function __contruct()

it should be __construct, the S is missing, meaning there is no constructor and the add_filter calls never happen

The function that registers the routes also never runs because the add_action call is commented out:

//add_action( 'rest_api_init', array( $this, 'extend_default_routes' ) );

This means the constructor never runs, and if it did run the extend_default_routes function would never be called, so the routes are never registered.