The routing is simple. Every node repeats everything it hears. A message goes out with a counter - defaults at 3, maximum 7. Every time it’s repeated the counter is decremented. At 0 it won’t be repeated any more.
You can DM nodes you’ve seen. You can create your own encrypted channels with a pre-shared key. You can link meshes over the internet through MQTT if you have an internet connected node on each mesh.