Don’t unsubscribe - that’s a signal of a live email address. Add a rule filing their domain straight to trash.

My understanding is that this is outdated advice.

There are definitely some vendors who respect an unsubscribe request, and some who don't. No way to tell ahead of time.

I won't buy, ever again, from someone who doesn't respect the unsub request.

In the UK there are legal guarantees, the unsubscribe button nearly always works.