I've seen this firsthand as well. I don't know that it was Facebook, but that was the only thing that seemed plausible at the time. My wife had been saying that she'd been getting creepy ads that appeared to be based on things she said out loud. I dismissed it as, "Oh, but you were talking about that because you read about it earlier, and the app noticed you read that story." She wasn't convinced.

Then we watched a random TV show on Netflix. During the show, two characters discussed a very specific medical method of improving their chances of bearing a child. Literally minutes later, she was getting ads for this type of conception therapy. We are both past child bearing age and have not discussed it in probably 20 years. We had never even heard of the specific type of process. We had never looked it up or read anything about it. It definitely came from something listening to our household, but we don't know what. It was way too specific to have been random chance.

We don't fall into the demographics for such an ad in any way. We have Apple devices with Siri, but that seems unlikely given their privacy policies. We don't have any Amazon or Google home devices (or any other types of their devices). She's on FB, and I'm not, so we think it was probably either her laptop or phone listening. She's had mic access on her phone turned off for Facebook and no other apps were running, but these apps have a way of finding their way around such permissions.