I run Mame4Droid and play old Arcade Roms like the street fighter series, or some NeoGeo fighting games, metal slug etc.
I've also got SteamLink installed so I play co-op games from my PC on my Shield like the Lego Marvel games.
There used to be some decent ones for the Shield TV but since all the games you can play on Android TV these days are just the mobile version you won't really find much that supports same device co-op.
I would look into emulators or some games on GeForce Now.
Try Stadia. If you don't want a console that is. It's google's gaming platform, and if you have a, for example, and extra xbox controller, you can probably play.
Example: Stadia has Mortal Combat 11. Two players. Beat each other up. Hours of fun.
Stadia is an app from Google Play store, and can be installed on Android TV.
limited selection of.....well, no AAA titles to speak of, but plenty to choose from to test it out.
Hey you can check out this article,here are some best multiplayer games you can enjoy on android tv. ( https://gadgetjunction.in/multiplayer-games-for-android-tv/ )
BombSquad.