I do this, and it does work, but it doesn't seem to learn that I don't want to see generic youtube garbage.

I'd love for it to learn that anything with a shocked face thumbnail and CrAzY question for video name is not desired.

Every so often I do that. I spend five minutes selecting channels I'm not interested in, because I watched a gamedev video once and now I'm being suggested hundreds of gamedev videos, or whatever. Pretty soon, it's like the algorithm just... gives up and starts suggesting me generic videos about celebrities and other vapid things that I'd never click on in a million years.

I often AM interested in a topic, I just don't want every little piece of content drivel shoved down my throat. I still want the cream of the crop to occasionally pop up in my feed.

That's the problem with marking things as not-interesting. The algorithm will wildly overreact in the opposite direction.

I've marked dozens of videos on a single topic as "not interested", only for them to be replaced by different videos on the same topic soon after. Marked all those as "not interested" again, and the next day there were more.

The only thing that works for me is finding the video in my watch history that's causing the recommendations and removing it there. Often it's even something I didn't watch all the way through or even gave a thumbs-down; apparently thumbs-down also means I secretly want more of this content?

YouTube's recommendation algorithm is somehow worse than useless.

The fact that feature exists shows that even YouTube know their algorithm needs help.