List of Gamevars?

Is there a list of Gamevars somewhere? If not, could one please be added to
the documentation.

That would be very useful indeed.

Hello, We’re not so sure about what you mean by Gamevars? An index of all
Simvars is available here: SDK Documentation
(flightsimulator.com)

Is this what you’re looking for?

No, we are referring to the SimVar.GetGameVar() and SimVar.SetGameVar()
functions of the various JS files.