This demo renders with WebGL2, which your browser has disabled or blocklisted.
If you're viewing over SSH X-forwarding or a headless / VM session, open it from a browser on a machine with a real GPU — e.g. port-forward the server and use your local Chrome.
Or force it: chrome://flags → "Override software rendering list", or launch Chrome with --ignore-gpu-blocklist --enable-unsafe-swiftshader.