> The ability for a website to see when you click on things outside of the page itself
It doesn't let pages see what you're clicking on outside of the page. That would indeed be a serious privacy violation. It merely tells the page that it's not on-screen any more. Personally I don't see any problem with that.
The person you replied to literally posted an example of it being misused:
> The ability for a website to see when you click on things outside of the page itself (either by changing active window or tab) is quite unexpected from an end-user perspective, and its use in various "ed tech" websites to detect alleged cheating
It doesn't let pages see what you're clicking on outside of the page. That would indeed be a serious privacy violation. It merely tells the page that it's not on-screen any more. Personally I don't see any problem with that.