The myth is that the devices are streaming audio back to be ingested into ad/recommendation algorithms, which is testable and generally not true.

I really wish these conversations would shift to the scarier truth: companies collect so much metadata on everyone that they can make pretty good guesses without processing what you're saying.

If you think "oh hey I was just talking about socks, how did they know to show me an ad for socks" it's likely because they accurately predicted based on your behaviors that you are highly likely to be in the market for socks right now.