It surprises me how many people aren't being proactive about their recommendations.
Hover your mouse over a recommendation you don't like, click the three dots that appear to the right of the title, click "Not interested". Results change very quickly.
When you aren't on youtube much it can be exasperating to manage this in this way. For example, I was watching a biology lecture on youtube. Recommendation tends to be insane conspiracy theories that include some words from the biology lecture title, and zero other high quality biology lectures. I'm not going to sit there and hover my mouse over literally every recommendation when they are all insane. I will just continue to not use youtube much, so far I haven't felt like I've been missing out.
Hover your mouse over a recommendation you don't like, click the three dots that appear to the right of the title, click "Not interested". Results change very quickly.