Greg
(Greg Stratton)
4
Are you running Roon build 363?
I have it working on my Apple TV 4K, tvOS 12.1.1.
On the Apple TV in Settings > AirPlay I have Allow Access set to Same Network and Require Password = Off.
In Roon, when you enable Apple TV, it will give you a 4 digit code on your tv screen, enter the code and press Return. That should enable it.
Cheers, Greg