You're still relying on sites fulfilling what they promise in a world where facebook has been blatantly violating gdpr from day one and enforcement just isn't happening

Set your browser to block 3rd party cookies, add privacy badger and ublock origin. It will have more effect than clicking "reject"

I click "don't send me mail" every time I buy something. Every place I buy from still sends me spam at some point. There are no negative repercussions for them beyond whatever infinitessimal thing me clicking the "report as spam" button does