YouTube keeps a watch history of every user. users can clean up their view of their watch history, but YouTube keeps it all.
if you watch any particular video, YouTube will start suggesting videos watched by other people who watched the video you just watched. YouTube does not know or care what the subject of the videos are. it only knows that people who watched a given video also watched these other videos.
there is ZERO intelligence, here.
if you want the ADHD recommendations to go away, remove any from your watch history.
your view of your own watch history (the list you can remove videos from) is what sets recommendations for you.