Hover a thumbnail on youtube.com and click an icon at the right: "Not interested" and "Don't recommend channel"
< Feedback on YT: not interested in one click
Found the culprit:
<yt-lockup-view-model class="ytd-watch-next-secondary-results-renderer lockup">
You might want a better way to hunt thumbnails in recommendations.
Nevermind I saw you updated
OK, found something interesting...
https://www.youtube.com/watch?v=oG5zUqJSqKY
The recommendations in this video do have the Not Interested In One Click features.
https://www.youtube.com/watch?v=q3BGJVz0PXY
But in this other video it doesn't
Perhaps you could trace the changes?