When viewing sites on iOS, at least, each Google Ad has controls at the top right of the ad image. Click the one that looks like a right facing arrow and you get an option labeled "Why this ad?" Clicking it shows why that particular ad was chosen for you. The same ads and option for viewing the "why" is available using Chrome or Safari browser.
I just did 3 ads on obxconnection so far and each had different reasons. Two said based on estimation of my interests. Read into that however you want, but I guess giving Google my data for ~17 years already and they probably know more about me than I do. One said because of browsing history in addition to estimation of my interests. One said "General factors about the placement of the ad, agreed upon by the publisher and the advertiser." along with "Information collected by the publisher. The publisher partners with Google to show ads." I assume those are blanket ads targetting a specific region or the demographics of the audience using a site/service? Dunno.
My wife is big time into using incognito tabs, minimal cookies, constant clearing of browsing data, and anything else she can do. She still gets ads, they are just less relevant to her. Since I've bought nothing, ever, from a website ad I don't care what they show me or how much they know about me.
On my work PC I'm all about blocking ads. I don't have time for them getting in my way. uBlock Origin does an amazing job. I use it with Chrome.