In Windows, the ads can be easily disabled. I still don't like it, but it only adds about 5 minutes to the setup process and then it doesn't bother me again.
Android TV's entire interface is ads, it gets worse with every forced update and there is basically nothing that you can do about. I'm looking for an alternative to my ancient ad-filled Nvidia Shield (which didn't have any ads day 1...), but I don't think anything else with a controller based interface can easily run Steam Link, Kodi, Retroarch, and still pass the DRM checks for 4k Netflix and Disney+.
Can you point me in the direction of how disable truly all of it? I don't want news/ads/recommendations in the start button, bottom bar, icon tray, search results etc.
Not entirely. There are many, many hidden telemetry settings that normal users can't access. It's why stuff like WPD (windows privacy dashboard) exist. Windows doesn't let you uninstall most of that stuff either.