While I do suspect they listen, I have pretty solid (anecdotal) evidence they scan text messages. When I bought my house I had no solicitor, I text my buddy to see who he used and he texted me a response.
Started to type into Google to get a number and it was the top suggested search after 2 chars. Nowhere else did I mention this solicitor, hadn’t heard of them before this, have no other searches for this solicitor. It’s not a big firm, it’s not even in my city - only explanation I have is they scanned the messages.
Playing devil’s advocate here - we know voice information is being sent back to both Google and Apple, if the analysis were done server side dissembling apps isn’t going to show us anything we don’t already know.