> Every interaction I have with a store or site signs me up for some promotional thing, which I unsubscribe from immediately, only to find it's one of 4 different lists I was added to.

Luckily this kind of thing is very much illegal here in the EU. If they send me marketing shit without my explicit active consent, they are in violation of the law, and I can at least report them. As I do. It is still not perfect, but the amount of spam I get from previous business relations has declined a lot in the past years. Other spam is still rampant, and I can only block any such sender until they find a new way to push their shit.