I find that a lot of them are something like 'lol', or 'love the way X did Y' / an unfunny meme (with thousands of thumbs ups) / something else along those lines. I find myself scrolling quite a long way to find anything insightful about what I watched, and just for something I can take with me in general.
The only video I found that sorta matches this is Chanel 5's ComplexCon video: https://youtu.be/jy9x09iCATA which has mostly meme replies.
Mentour Pilot made a video about a 747 crash https://youtu.be/Y50saxfTqQA and the top reply is from a pilot with a lot of the other replies being from pilots as well.
And the last video I looked at was one titled "All 8 Species of Bear" https://youtu.be/7DERN0R3AbM which I thought would definitely have trash comments because it seemed to be from one of those "Top #" click bait channels. But the top replies are bear stories, species information, and some zoologists. No idea how accurate the info is, however.