It's usually Samsung people talk about with regards to spying on Smart TV, and reports saying they send regular screenshots home for analysis.
I don't know if LG does the same, but in terms on ads in the display I ... never really found it to be anything.
I sold my 55" LG OLED highend model last year when moving, but except for a "recommended app"-showing on the main menu I don't recall any nag-ware. I also found the smart TV features to beat most, if not all, dedicated boxes in speed and usability and preferred it to Apple TV.