Best I’ve got is sloths. And they’re only green because algae grows on them. And I know it sounds like cheating because they aren’t intrinsically green but before you completely discount it there are animals that wouldn’t be the color they are in a different environment. For instance, flamingos are only pink because of the seafood they eat. If fed a different diet they can be almost white.
I know a bunch of these do the annoying YouTube thumbnail thing that is very much adjacent to your complaint but I would argue they do a pretty good job of being excited about the topic but not overly dramatic in the presentation during the actual video.
General topics:
https://www.youtube.com/@Wendoverproductions
https://www.youtube.com/@halfasinteresting
Science
https://www.youtube.com/@SciShow
If you just want to learn about astrophysics. Many build on each other so you might want to consider watching a bunch of the early ones first.
https://www.youtube.com/@pbsspacetime
Engineering. This guy’s voice annoys me but some of the videos are still quite interesting so I linked this specific one about exactly how train wheels/tracks work. Never would have guessed the level of design involved.
https://www.youtube.com/watch?v=Nteyw40i9So
This is an interesting question but I don’t think it is restricted to green. Isn’t the same true of purple, blue and red? I’m not talking about just reddish like human hair or a red panda but truly bright red like a cardinal. I would imagine it has something to do with our evolutionary history. Complete speculation here but laced with a few facts I picked up. I hear the common ancestor of mammals emerged around the time the dinosaurs became extinct and was basically a tiny rodent like a shrew. I wonder if as a small animal that can’t fly or swim it had to hide a lot and basically just came in shades of brown. So maybe any genes for other colors were lost before that common mammalian ancestor emerged and although mammals have lots of patterns they don’t have many colors.