Android TV doesnt have pop up ads.. It must be one of your apps
Try sideloading Blokada 4 (has to be 4). It's a bit clunky, it was designed for phones, but it works on Android tv too. It blocks app' ads.
Download it on F-Droid.
Check your notification settings. Probably it's from some app/game you installed.
Android TV doesnt have pop up ads.. It must be one of your apps