I occasionally see a small, easily ignored, ad tile on the "Home" banner at the bottom of the TV at power on.
The ones in the Universal Guide are bigger, but tbh I think I've only used that once or twice since having the unit. I watch live TV so infrequently that for the small amount of it I want, I know the channel and time without needing the guide...
I did also go through the settings quite meticulously, and disable everything relating to "telemetry". It gets re-checked every time the TV claims to have "updated the firmware"... because I don't trust them not to have changed that setting on the sly.
(When I went to check this just now, the ad I was served was for a Samsung TV... which seems redundant...)