Those are either emergency lights to flood the ship in the event of a situation, or heat sensors monitoring for fire. I don't know the timing as to when those were added, but they are not wifi related, medallion related, or a camera.
The boost in wifi coverage out to the balconies is due to the in-room wifi router. When each ship was updated with Medallion technology, the new tvs that went in place are hiding a small wifi router behind them. This is the major boost of connectivity we've noticed since 2018/2019. Prior to that, the routers were only in the hallways and would struggle getting a signal through the heavy metal/fire proof cabin door.
In addition to the in-room routers, there are medallion sensors overhead in the bathroom, cabins, and balcony. But the one on the balcony is a lot smaller than this emergency light dome, and fully enclosed in opaque plastic (and all medallion wiring is purple too if you haven't noticed).
Again, not sure if its for additional emergency lighting or for fire monitoring (since the Star Princess incident in 2006), but I can confirm its not a camera, medallion sensor, or wireless access point.