The other questions on this subjects are 4-6 years old and have not helped to solve my problem playing my media from a Mac to an Apple TV.
- MBP Retina Early 2013 running OS 10.12.6 (Sierra, current)
- Time Capsule (don't know how to obtain model or software level)
- Apple TV (Model A1625, tvOS 12.0.1, current)
- MBP <-> Time Capsule <-> ATV connections are wired, not wifi
- MBP <-> Time Capsule is via a Thunderbolt/ethernet adaptor.
- MBP and ATV are on same local network, 10.0.1.x
Every time I switch MBP 2013 Sierra Sys Pref > Displays > AirPlay Display from Off to Great Room (3) (no idea how the subscript got there; there's no Great Room (1) or (2)), the setting holds momentarily and a modal dialog comes up asking for some color settings before vanishing and returning the AirPlay Display back to Off.
Meanwhile, I can send audio from my MBP 2016 Mojave over wifi to the Apple TV just by clicking on the loudspeaker icon in the menu bar and switching from Internal Speakers to Great Room (no subscript here). So obviously there's nothing in the ATV actively preventing AirPlay to it.
I have also tried switching the MBP Sierra's network from ethernet to its wifi. This appears to make no difference.
While sending the audio from MBP Mojave to ATV, I go to the Sierra MBP Sys Pref > Displays and again try to switch AirPlay Display to Great Room (3). This immediately kicks my laptop audio off of ATV and back onto internal speakers. So clearly the Sierra MBP is getting through to the ATV to a certain extent, kicking the current user off, but is unable to complete the process.
There must be a lot of other clues, too, but these all seem significant. It seems to point to a problem with the MBP Sierra, since it can't even connect to ATV on wifi. I'm out of ideas. Any suggestions?