The Phoenix LiveView approach is tightly coupled to Elixir, which makes sense given some of the unique properties that Phoenix, Elixir, and the Erlang VM provide.
Communication is all done via web sockets. The system has built in presence and PubSub capabilities, which enables a lot of cool applications.
LiveView systems should scale really well, thanks to the underlying framework.
This What Is Phoenix LiveView is a quick, 4 minute, and well done introduction. And explains what these new Server Side Rendering frameworks are solving for, even when they each take a slightly different approach.