The very notion of proof implies that you can reproduce it. So I would suggest you forget what anybody here or elsewhere said. Instead, you :
- get a cheap phone (so typically Android)
- reset/format/flash it to a blank state
- make a new testing account on it
- use for random browsing, using app, etc and you log your history, namely what did you actually do AND what ads you actually see
- test for something outside of your new habits with a search query, then log and compare again, seeing the threshold to change
- repeat the last step for something said using e.g. a voice assistant, log&compare
- repeat WITHOUT explicit search, log&compare
Yes this takes a of time but that will help you make YOUR own opinion on the matter if you genuinely care.