I have a sony as well, and you can use it as dumb TV, by not agreeing to their privacy policy. If you want to connect it to wifi afterwards, it points you to the privacy policy again, so it seems like the TV follows that. But I've also purchased it 4 years ago, so not sure what the status is now.
So far, I've seen no ads. I mostly use it mostly via HDMI and sometimes for watching freely available TV via antenna.
*attempts to fathom terrors* *suddenly gets urge to put on a maid outfit and dust the place* You're not wrong...