AppleTV was working at one point and stopped after the last major Roon update. I didn’t use it much but just got the new AppleTV and wanted to finally fix it. I setup the connection in Roon, enter the 4 digit code to pair. On the Roon side it looks successful but the code doesn’t disappear from the AppleTV like it normally would. If I attempt to play anything, the code pops up again.
Roon is known not to work with the 4-digit passcode approach (and it would be great if they could somehow fix that). In the AppleTV under Settings > AirPlay and HomeKit, make sure that Allow Access is set to ‘Require Password’. Then enter a alphanumeric password of your choosing.