- I talk about something with friends, for example a pair of new shoes. I never search for shoes online and never online ordered. Next time I open instagram I get ads for new sneakers.
- I talk with a friend about depression and mental conditions, next thing I get ads for a new online counseling app.
This happens with friends using both Android or iOS. We are not on the same wifi network and don't talk about these things online through messengers. I don't have facebook installed (but have instagram and messenger). I am a somewhat cautious person and besides very rarely checking instagram or replying to messages barely open either app.
One theory is that someone at a later point searches for it online and through GPS approximation and social graph the network makes the link back to me. But besides that I have no clue. Always listening through microphones is a far stretch especially given security models and APIs on iOS.
The chance of such alignment may be significantly higher than our intuition says, a bit like the birthday paradox counterintutively has a >50% probability of happening.
Another option could be that you've searched or browsed content about this before so you were getting these ads occasionally anyway but didn't pay attention to them until you talked about it and now that ad stands out.