If I ask Google how many computer companies are a certain nationality, a bit later I get an email regarding that topic. Does that mean I am being monitored? Coincidentally, I am also getting tons of spam.
It is too much of a coincidence that it is by chance.
Any type of rewards program, that data is likely sold to data brokers.
Many websites send data about you to companies like Facebook even if you don't have an account and can potentially identify you
Tracking pixels and images in lots of sites send usage data about you
Going to the doctor's
Even if you didn't own or use a computer you'd still likely be trackable
the phone, gas, school and medical are all online and normally pretty simple to get access to + the gov tracks [tax, votes, licence and fines] - they don't normally actually sell this info like Google but they also don't put any real effort into keeping it private
most people with a phone have recording of their voice stored asking questions or just random talking their phone recorded incase you asked it a question... in special cases individuals are tracked like russan generals being killed because their mobile phones give away their location to sniper teams but on the whole its just worthless junk being stored by dum people because they can get away with it