Presume that duckduckgo is not private or otherwise compromised.

For example many things I search trough duckduckgo later that day showed up in my twitter/x.com algorithmic feed, coincidence ? don't think so.

Or it could be that, when you search something, you also click through to some of the results, where FB/AdWords and other trackers are present.

Alternatively, there was a fallacy of human mind(forgot the name), where if you think of something, your brain will start focusing on the random occurrences of that things in all places. So, those ads were always there, your brain just started focusing suddenly on those as you were thinking of those things.

Note: Not affiliated with DDG.

Yes, in this case only way to not be spied on is to not go on the internet

https://en.wikipedia.org/wiki/Frequency_illusion

It's called the Baader-Meinhof effect.

duckduckgo don't prevent website to track you or deposit cookies etc. Once you're on a website, let's say twitter, duckduckgo does nothing.

> When you view Twitter content such as embedded Tweets, buttons, or timelines integrated into other websites using Twitter for Websites, Twitter may receive information, including the web page you visited, your IP address, browser type, operating system, and cookie information. (https://developer.x.com/en/docs/twitter-for-websites/privacy)

So, if you visit a news paper that have embedded twitter post in it, twitter might know you passed by this website.

There's also the likelyhood that the pages you landed on sent your info to their "ad partners"