Working through the steps (checking that the Info,plist matches exactly), run the demo game and what appears is grey but does not fill the landscape screen when run in the simulator against an iPhone 11 Pro Max (as recommended earlier in the text). This may be an Xcode related problem. I have noted occasional problems with the menu bar not going away but this time the actual grey box is not filling the screen - it actually looks like a scaled down iPad screen. It works correctly on any of the iPads that I tested.
Xcode 12.0 beta 4 on MacOS 11 (20A5343i)