So almost every GDPR cookie consent banner out there has a section for “legitimate interest” cookies that they can leave on by default and you will inadvertently accept even if you choose “Reject all” unless you go to the detailed settings and disabled those too.
Some of them have dozens of legitimate-interest cookies.
I read some articles about what they are and why it is allowed to keep them on by default, but they were very vague. So can someone explain it to me like I am five?
I think that they ignore that second point.
Advertisers have a legitimate interest to process your data and they use the legitimate interest option to do so completely ignoring the fact that they need to infringe upon your privacy to do it.