Yup, as I have found out over the last 5 hours. I managed to get a handshake but it's nowhere near the convenience of something like WebSockets. The security circus you have to go through to get even a handshake working is absolutely absurd, all sorts of extremely poorly documented certificate requirements and you'll be lucky to get an error message that helps you in any way. I'm getting ready to give up for the day, I will definitely make a top level HN post if I get a solution working and documented.

Meanwhile https://github.com/achingbrain/webtransport-echo-server this is the best we have for a minimal working node example.

Surprisingly, socket.io supports WebTransport: https://socket.io/get-started/webtransport

The guys at Colyseus (a JS library for multiplayer games netcode) also added support, in a preview version for now.