On a video in a video list page there should be a “…” menu next to the title. It has options for “hiding” the video and “don’t recommend channel”. I can’t comment on how effective those are, but they might give the algorithm some hints about what you want to watch.

In addition, if you have stuff on your watch history that you don’t want to see more of, you can go to https://www.youtube.com/feed/history and remove them. Allegedly that stops them being used to decide what videos are recommended.