That looks like a typical JSON definiton with nested components. I’m pretty sure that the Android Library, either Java or Kotlin would have library methods available to convert the JSON to a Map. I don’t know the meaning of “rendered”, but it does look like a key to a map.
It looks as if there are post titles there, but don’t see any content. Maybe you need different parameter values for your JSON request?
I have never needed to dig into any WP APIs to get post content in JSON format.
After a second look, it does seem that your returned JSON is returning Post IDs, a Post Title field that has actual title string included as a “rendered” element. Looks like nested Maps. You should NOT think about stripping anything, but converting the JSON to an appropriate structure (I’m guessing a Map). Then you can extract the title. There’s probably an ability to fetch the post body in the JSON data as well.