It passes through your navigator.platform, userAgent and screen dimensions, from the client you connect with. But this is not necessarily the actual values of the machine you run it on. So the site you're browsing thinks it is talking to a browser on, say, an Android phone, but actually it is (in the live demo anyway) talking to a browser running in a virtual Debian instance in GCP.
For fun, check out your geolocation. That is not passed through
For fun, check out your geolocation. That is not passed through