Here's a repo to get you started, though you'll need to either do some workaround in SteamOS to get it to stick since it is immutable (Steam Deck/Machine community has a couple ways of doing it), or use a regular game optimized distro like CachyOS: https://github.com/WayDroid-ATV/waydroid-androidtv-builds
Make Android TV shortcuts for apps that don't normally work on Android, but have gamepad support: https://atvlauncher.trekgonewild.de/
You could also just do regular Waydroid, but some apps won't give you the TV optimized version with gamepad/remote support, then you need to use something like this or Mantis: https://github.com/keymapperorg/KeyMapper
Never connect your display to the internet is the classic advice.
Unfortunately some screens require you to connect to a Wi-Fi before they let you use them, causing you to need to create a unique burner hotspot on your mobile device to complete it. We've also heard of these kinds of devices connecting to any open network automatically too.
I can imagine from TVs and mobile devices these manufacturers have a database of Wi-Fi network + passwords it could use as well. Screens are also integrating docks into themselves meaning that Ethernet meant for your laptop or connected to your desktop could be used too.