As everyone is saying: just don't let it on the network. It's a little annoying because you can't have smart home stuff like "turn off the TV when I leave the house" working, but that's it.
My thing is, don't use an Apple TV. For the last 15 years or so I've just used a Mac Mini plugged into a big TV, and it's perfect. Get a wireless keyboard and trackpad and one of the many available trays that will hold them together. I'm literally typing this right now on this exact setup.