I'm a news junkie, I think paying for news is important, but I don't have even 1/4 of the subscriptions I would have if it wasn't for scummy tactics and/or the fear that I will be subject to them in the future.
FWIW, from 2022 on, Germany will have a 2-click unsubscribe law [0]. It requires clearly labeled buttons and forbids a lot of dark patterns.
[0]: https://www.mofo.com/resources/insights/211006-new-two-click...
Many countries that don't have that will have consumer protection laws that simply get ignored, because simply ignoring them works for the company.
Recently many companies are (finally) allowing to use the PEC (which is a form of Certified Electronic Mail) which has the same legal value as the registered mail, but that the average citizens do not have (unless they have it for other reasons), which however has a (small) yearly cost, but that may be "dangerous" in the sense that it becomes your "legal address" so it needs to be monitored as anything that arrives there has legal value and is considered delivered to you the moment it arrives in the inbox.
Oh you require it by certified air pigeon? Great, happy to; pay for it.
Though I haven't had issues in cancelling stuff. Online services work nicely for all other stuff.
The rationale is that you could claim that you received the letter, but upon opening the envelope you found just some blank sheets, with the piego there is no way to deny that it has been received.
And viceversa, there have been cases of envelopes sent intentionally with blank sheets inside, only to get the receipt and then be able to claim that "document X" has been sent within a required deadline (and actually fabricating the document later).
They might have changed. When I checked just now, they offer a phone number and an E-Mail address to cancel a physical paper subscription (there's no account, so that makes sense).
An online "Spiegel+" subscription can be cancelled via their website.
https://abo.spiegel.de/de/c/abo-service/spiegel-abo-kuendige...
It may be different for their non-German publication, but I had trouble finding any English information - which may be saying something...