Runway not sloped
The sloped runway feature that has been implemented by Lockheed Martin in v5 is essentially for default runways and how AI react to them. It still requires developers to create complex 3D models for a sloped runway, it's not a simple switch to flick.
As the simulator progresses and functionality is exposed to developers, we will embrace this and implement sloped runways. Until then, please check the product description to see if the airport includes a sloped runway.