I am running the Roon Core on my mid 2015 MacBook with Mojave 10.14.6 OS. I am current with Roon but actually I could not find where to check the Roon version.
I have two Apple TV’s that are not yet Roon enabled. One is enabled and working fine. When I try to enable, Roon is asking me to enter the AirPlay device password and Roon is not displaying a password. I have AirPlay turned on (on my MacBook). I tried entering various ps but I thought AirPlay generates one dynamically that can then be entered.
On the Apple TV, if you go to Settings > AirPlay and click on Airplay Everyone, you will see Security below. This might show Require Code First Time Only but should be changed to a Password. Can you give that a try and let me know if it corrects this behavior?