Apple TV not showing up in screen mirroring

Hi,

Idk if you fixed your problem, yet. But here you can find something useful from the official Mac support: https://support.apple.com/en-us/HT204291.

Hope you can solve your problem and enjoy your Apple TV!

Cheers

if your wifi router does not have wired ethernet/ wifi 2.4Ghz and wifi 5Ghz bridged as 1 network and the devices are connected to different ones it could explain it