How do they track me?

I used DDG through Brave browser on my phone to search most expensive D&D cards (I was never into D&D and had no interest in this topic whatsoever. Searched this because the topic was raised in a in-person conversation, so decided to check).

A day later I get D&D ads in Reddit (I have Reddit app on my phone).

Please help me understand how this connection had happened and how come I received this targeted ad without any previous history …

ads amp brave brave browser browser check conversation interest phone privacy reddit search topic track