[bensecure]

If you open your google account settings, the very first section is labelled "privacy and personalization". If you click on that, the option to disable youtube watch history shows up. In terms of "dark patterns", they do have a nag prompt begging you to reenable watch history which shows up in the recommended videos section of a youtube video. The only way to disable this nag permanently is seemingly to block it with uB0.

[outsidetheparty]

Yep, I was looking in YouTube settings instead. I wouldn't have thought to leave YouTube to change a setting that affects YouTube, but it's a reasonable-in-hindsight design decision to collect all the privacy stuff for various google apps in one place.