Usually that means trying to get Android TV working through USB, but it depends on what tv you have. If you already have an Android TV, just use a launcher like Projectivy. Most people just buy a media box: either an Android based one or apple tv and disable the "smart" tv altogether
I'd imagine you could probably get into the android developer settings and disable all the telemetry stuff through adb and install a custom launcher like projectivity and that'd be the closest you could get to running a custom tv OS at least if you can't flash it.
It's better than dealing with whatever terrible nonsense they put on LGs and Samsungs. I was really close to getting an LG because everyone says it's the best looking but I just couldn't imagine going back to completely unmodifiable TV OS, so I got the Sony instead which still looks absolutely fantastic and I have my custom launcher on it set exactly how I want it.