I cofounded Hathora (https://hathora.dev/) last year and we've been working on making it easier for smaller teams and individual developers to build scalable multiplayer games. We think the serverless model is the simplest approach, allowing you to dynamically provision a new instance of your game server when users or your matchmaker requests a new session.

We made this .io style demo to showcase this approach, and we're releasing the source code and documentation alongside with it.