To save you some time: Google and Meta are monitoring the conversations using the device’s microphone

This is not happening. It is not something that would be possible to hide, there are so many different places this could (and would) be detected by someone with the right know-how (data/battery consumption in particular).

Try and pay attention to how many ads you get that are completely irrelevant to you. It will happen way more often than ones that match up with your conversations.