I can’t think of other examples, but this exact problem is a constant frustration for me on multiple sites. I can’t scroll with my cursor on the page without crap happening that I don’t want to happen.

As to the reason, at least with Youtube and Facebook, the answer is obvious: they want to increase their ad revenue by claiming additional “plays” or “interactions” or whatever they want to call it today. I remember realizing several times over the years that I had been conned when I paid for ads. The top-level numbers looked good, but when I dug in, I realized they were all faked.

You can just... turn it off: https://www.youtube.com/account_playback

I have it turned on, but leave my mouse to the right of the screen if I don't want autoplay. It's habit now.

Put your mouse up in the header on or near the scrollbar, scrolling will flow below to the video list.

It's even worse on mobile. You don't even need to hover for an autoplay video to show in your history.

This may be a dumb question, but when you have video doing autoplay (as in the video starts playing while you're scrolling looking at multiple videos - you haven't clicked on one), does it show up in your watch history?

Because of excessive things like this, I often point at my screen with a pen now and leave the mouse alone. Or take notes on a different laptop to avoid this stuff.

This drives me absolutely nuts on Netflix too, perhaps more so.