Blocking the notice (or ignoring it) is technically equivalent to opting in. Of course, if you're using a competent ad blocker it's likely that the trackers themselves were also blocked, making this a non-issue.
* it's hard/impossible to prove - given how many factors go into ad targeting there isn't a conclusive way to prove whether an ad was targeted because of illicitly-collected data.
* as you see here even blatant GDPR breaches and acting in bad faith doesn't actually land you in trouble, so although it's "illegal", the law isn't enforced. Experian (or Equifax) got caught by the ICO knowingly misusing people's credit data for marketing purposes and all they got was a warning, so clearly the message is that "breaching the GDPR does pay".
Then, also enable uBlock origin's "annoyances" filter.
It does appear (from their website) like the aforementioned Stardust can auto-decline everything, but I haven't tried it myself.
One problem you run into when declining cookies is that on many sites you won't be able to view embedded YouTube videos, tweets, etc. unless you go back in and allow social media cookies.