Every few days if you notice the algo giving too many fast-food style videos, it's worth it to aggressively use this to unfollow all these topics. Miraculously, the next time you refresh your feed, all those old interesting topics you used to be into will come back.

Overall the algo is very very recency-influenced. You can watch videos from a niche interest for a year straight, but if you then spend a week watching nascar, you'll never see anything but nascar videos for months unless you say "not interested".

I imagine they have found that for the average user, having a longer history doesn't improve G's metrics.

I wish the algo would instead notice that I always watch every video from particular channels that only publish rarely. I also publish my own videos, and after a long gap without publishing my new videos get no views unless I pay for ads or promote them outside of YT, and even my family members who are only subscribed to my channel don't get my videos recommended.

This is useful but it's pretty opaque to the user as to what exactly this does.

It tells the algorithm that you’re “not interested” in videos like that one?

Yup, that's what I always do, and unsurprisingly my recommendations are great.