How do websites (e.g. slickdeals.net) provide very personalized ads when tunneling is on (ip is changed) and cookies are disabled?

I recently bought an apple watch, office chair, and a prepaid SIM card. All these are labeled as "personalized" on slickdeals front page even when tunneling is on (ip is changed and no leaking), ad blockers are off, and all cookies are disabled.

I am wondering in general how this is achieved, if this is something I should worry about, and if so if there is anything anyone can do about it. Is it in any way helpful disabling JavaScript …

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