Have logged in to stop this from happening and currently apparently I'm "Open to discussing new opportunities", which is news to me. On trying to change it to "Not interested in any new opportunities" there's a dropdown that says "I’d be open to new opportunities in:" and most you can set it to is 2 years. These are whole new dark patterns.
UPDATE You can turn off the setting they're talking about by going to [0] and then clicking the little grey "Visibility settings" under the Profile URL section.
UPDATE There's a delete your account option on this page [1], though YMMV:
>> Government identification may be required and we may ask you for more information in order to verify your identify
They have definitely been kind of spammy for a long time...I usually ignore their emails but I actually read the first paragraph of this one and it sounded like it was an opt-in feature, so I closed it, but the important line was further down: “You can edit your profile privacy settings to not appear in public search engines at any time.”