Iirc one publication email would have an unsubscribe, but it only unsubscribes from that publication. There weren’t options to unsubscribe all from that button. For that I had to sign in and it wasn’t too easy to find the unsubscribe all option.
I've done it a few times, its suprisingly quite nice. They generate a unique email you can forward the offending message to
When you sign up to get emails form a specific author or publication you’re signing up to that specific newsletter, delivered to you by Substack.
Anyway there's other stuff. Via CAN SPAM laws, companies cannot pre-check subscription boxes (Substack does this in onboarding as well as when you subscribe via browsing their site). [0][1]
Also their consent gathering is not up to par. The regulations "require that a request for consent must contain a statement indicating that the person whose consent is sought can withdraw their consent."
Last, there may be something about how Substack bundles subscribing to publication on their dashboard into emails. To me this isn't unlike how following on twitter can't automatically subscribe to newsletter emails. There's specific callouts in CAN SPAM about such bundling. Ie you can't bundle accepting terms of service with receiving emails.
[0]: https://crtc.gc.ca/eng/archive/2012/2012-549.htm
You’re not receiving a notifications for content to be consumed on Twitter or on Amazon.
As for the other things you mentioned, those are more legal things I know absolutely nothing about and so I won’t comment on them because I honestly don’t have anything to contribute.