The original cast-only chromecasts didn’t have ads as far as I know, but they’ve all been discontinued and replaced by the google tv chromecasts which have ads integrated throughout the interface, mostly just for streaming services, movies, etc.
Fuck seriously? I have a Chromecast from like 7 years ago and I was considering getting a newer model just because, you know, improvements and stuff. But definitely not if there are ads. Holy shit no.