Mac OS Music App only showing old Apple TV.

AirPlay from the Music app is as described in Use AirPlay to stream audio - Apple Support.

You don’t have to screen mirror to use AirPlay, if you use the in-app AirPlay controls.

It doesn’t matter if you use ethernet or Wi-Fi or any combination thereof, as long as your router configures all of it as one logical network, without blocking the needed ports.

Obviously AirPlay has to be enabled on the Apple TVs.

Hi stadtler,

We understand you'd like to use AirPlay to connect your Mac to an Apple TV. We're happy to help.

If the Apple TV isn't showing up as an available device when you click the AirPlay icon, we'd recommend checking these things to start:

Make sure the Apple TV and the Mac are connected to the same Wi-Fi network. If you have a dual-band router, make sure they are both on the same band. For example if your Apple TV is connected to the 5 GHz band and the Mac is connected to the 2.5 GHz band, this would technically be two different networks, even if you have them both named the same thing. You can access the Wi-Fi settings in System Preferences > Network on the Mac and in Settings > Network.

You'll also want to make sure you have the AirPlay option enabled on the Apple TV. You can find this option in Settings > AirPlay & HomeKit.

Manage AirPlay settings on your Apple TV

If both devices are connected to the same Wi-Fi network and the AirPlay option is enabled on the Apple TV, you can try restarting both devices as well as the Wi-Fi router.

Log out, sleep, wake, restart, or shut down your Mac

Restart Apple TV

Most Wi-Fi routers don't have a power button on them. The easiest way to restart them is to just unplug the power cable for a few seconds.

Use AirPlay to stream audio

We hope this helps. Cheers!