Possible to edit react native source code?

Is it possible to directly download the react native source code of my app, so I can add in additional functionality to my app that’s not currently available on the thunkable?

No it is not. Each of the components are double programmed on the back end to support either Android or iOS.

It is not Javascript react.

If you want to customize you can do so with classic (app.thunkable.com) and use Java to create an extension.