My kid is 5. We don’t hand her screens as toys/babysitters, and she has never watched YouTube without supervision. Even when we watch together, we don’t put it on autoplay.
One time I decided to search for Happy And You Know It in Spanish, so we could learn to sing it together, and a video came on where everything was creepily photo-negative and then there was a close-up of a fast-moving pile of worms. I turned it off immediately thinking WTF did my kid just see?
I am troubled by the same things as you. I’m so glad to read this and to see so many other people have clapped for it.