I bought a android tv device (NVIDIA shield) and just assumed it was open source like android, turns out it's not and they force ads on the home screen, if you jump though a ton of hoops to roll back some updates, you can turn them off, but it will re-enable them after a while. does not feel like a device I own. Even NVIDIA cannot turn off the google ads on the NVIDIA shield. you can add other launchers but they don't make it easy and they regularly get removed as the default launcher.
At this point I'm just considering just making a mini PC with linux https://plasma-bigscreen.org/ that will stay connected to my TV. OSMC is another option; however, it does not work well with DRMed content, so I gave up on that as well; even though it's an awesome project. Some android TV boxes are compatible with Lineage OS so that might be another option.
Believe you can also remove the stock launcher on the Nvidia Shield. Have not done it myself, but have also never had my launcher automatically change like you mention. I'm using ProjectIvy🌻
as a player, Streaming boxes that have an Android OS are great but Google Supplies Android TV as the default launcher with those devices which has gone downhill for a while now.
80% of your UI is now covered with Ads.
So if you switch to something like an Nvidia Shield or something like that definitely use a different launcher instead of Android TV. I currently use the Projectivy Launcher which is so god damn clean and only contains what I want to see.
I just wish they fixed the subtitles, then I would actually use it. In most situations It's totally unreadable unless you turn on the black background, which is ugly. How hard can proper shadowing be? Everyone else does do it correctly.