Chromecast with Google TV

How To: Sideload Apps on Chromecast with Google TV — Get Virtually Any Android App on the Big Screen

At launch, Chromecast with Google TV is fairly limited in the number of compatible apps. Many of the usual suspects are there, but there are some interesting omissions, like Google Stadia (though support is coming). However, at its core, the device runs on Android 10, which means you can sideload apps, including those that don't officially support Chromecast with Google TV.