Hacker News Reader

It is more important to scrub your history and upvote.

You can use ublock to remove the sidebar completely

Unhook also does this (among other YouTube clean-ups)

In case you start watching such a video (and maybe in general), it’s probably more effective to downvote it and remove it from your watch history. And when you use “not interested”, there are two “tell us why” follow-up options “already watched” and “don’t like”. Selecting the latter may be necessary for “not interested” to have a stronger effect.

I don’t know if YouTube Premium makes a difference, but I don’t see highly clickbaity thumbnails very often.

It seems to help. But it's just one factor. I also have a lot of subscriptions to help guide the algorithm. And it seems most heavily weighted on things you've recently watched, so if you ever leave youtube playing while you're not actually watching it, you might need to manually remove videos from your watch history that don't align with what you want to see suggested.