What are some ways to train, test and render an RL autonomous drone in a simulator?
I tried contacting a few drone simulator makers including DRL (Drone Racing League) and Velocidrone but the latter does not have API for Python and DRL has not responded.  

Therefore, I looked at Unity ML Agents and saw that it's possible to create a simulation environment using free drone assets:

https://unity3d.com/how-to/unity-machine-learning-agents

https://assetstore.unity.com/packages/tools/physics/free-pack-117641

And they have a Python API:

https://github.com/Unity-Technologies/ml-agents/blob/master/docs/Python-API.md