Profiles, not microphones
Advertisers buy audience segments built from search history, app use, location patterns and purchases. Coincidences feel uncanny because the profile is accurate.
The auction
When a page loads, an automated auction sells the space to the highest bidder for you specifically. It finishes in well under a second.
What you can change
Ad personalisation settings, tracking permissions and cookie choices all reduce the data available. They do not remove adverts — they make them less targeted.