I have the new 16in with the 5600M card and installed windows 10 with bootcamp last week. This is the same driver that is installed when you install bootcamp ver 19.50, so looks like AMD is just making it available on their site.
The odd thing is that I had the 16in with the 5500M and was blown away that you could actually run SteamVR on Windows in bootcamp and get pretty decent performance. I played Half-Life Alyx and Superhot VR both performed really well! Here is a YouTube video reviewing SteamVR on the 16in with the 5500M.
***So here is the annoying part***
On the new MacBook 16in with the
5600M I cant get SteamVR to run smoothly at all! The driver wont let steam put the HMD in Direct Mode, and looking side to side in VR is super jittery.
Not sure what is going on, if this GPU is just not going to be great for VR, or if the driver needs to be optimized, but the 5500M had no issues.