if you need access to the request parameters, the route name, or the route object itself, use RouteMatch.
like for example a user ID, you can access the data using:
$request->attributes->get('_raw_variables')->get('user')
or better you should inject the 'current_route_match' service or you can use \Drupal::routeMatch()
Example
$route_match->getRawParameters('user')
