I do not know a lot about the ad mechanism, which my partners use. But it usually works by contacting several servers and asking them "hey, there is someone visiting www.Photopea.com, probably from Canada, with a screen resolution of 1920x1080 pixels, how much would you pay for showing them your ad?" ... there is an auction, and the ad from the highest bidder is shown to you. The more servers take part in the auction, the more money I can make.
Like really, if you open a website for the first time in your life, what kind of secret information could it know about you?
The trackers in your site use cookies, and browser fingerprinting to create a profile of the visitors to your site, which combined with other data on the visitors is used to identify them personally.
That on its own should give you pause. But that data is then used by companies like Facebook or Google to allow the highest bidder to alter that users behaviour - by getting them to believe some propaganda, to vote for a political party, or to spend money on something they don’t need.
That’s the business model. That is how you make money on your site.
There are other ways of making money – I’m sure that had ad revenue not been available you would have found a different way.
Like really, if you open a website for the first time in your life, what kind of secret information could it know about you?