Oh my gawwwwwd building a game to Xbox with Unity is a horrrrrrrrible process. Getting set up is a messy, messy process backed up with sparse, outdated or flatout broken documentation both on Unity and Microsoft's side.. it's awful. I don't recommend this to anyone. Use another engine, use another console.. just avoid this lol
Apparently I need both Visual Studio 2017 *and* Visual Studio 2015 installed to be able to build to Xbox from Unity. What kind of broken mess is this, and where am I supposed to get a working version of VS 2015 with extra c++ tools ?! Such a mess.
Alright so it turns out one of the reasons Unity to Xbox was messed up was because I was led to believe that I needed the XDK forum but I actually needed the top secret GDK forum. Now I'm in the GDK forum I think we can download the right stuff to make a build without needed Visual Studio 2015 (!?) .. sooooOOOOoooo yeah I'm still trawling my way through it lol We'll get there!