There's a known bug of this and I was directed here by support.

I have found a work around to get Waze navigation to work on the vehicle display through Android Auto.

These steps, in this order, will allow Waze navigation to function on the vehicle display. The steps must be performed each time the phone connects to the vehicle. So switching from wireless Android Auto to wired and vice versa will require following the steps again. All steps are performed on the vehicle display unit, not on the phone.

1. Open Google Maps on the vehicle.
2. Start navigation in Google Maps on the vehicle, destination does not matter.
3. Open Waze on the vehicle.
4. Start navigation to your destination in Waze.
5. Switch back to Google Maps on the vehicle.
6. Terminate the navigation on Google Maps.
7. Switch back to Waze on the vehicle.
8. Enter your destination, the routing should be displayed properly now.