Here is the Dutch implementation, because it's the first I could find in English: https://business.gov.nl/regulation/automatic-renewal-subscri... As is says there "Consumers must be able to cancel their agreement in exactly the same way as they signed up for them."

It's based on an EU directive, but a recent one so not all countries have it live yet. More details on the EU directive and the German implementation starting next year: https://www.mofo.com/resources/insights/211006-new-two-click...

IIRC it's a law that is just a few months old.

That's not really a source.

It's a possible explanation for older anecdotes about having to cancel by fax.