Oh, sure, those are indeed major fails in all of the OSes - no guides and no easy way to find anything about fundamental operations (it should be easier than googling).
But these are separate issues. For example, even with the scrollbars there can be a change between two behaviors: click on the empty bar jumps to that % or jumps by 1 page. And one can be a click and another a Shift-Click - where in the OS would you discover that??? And the scrollbar width - can only find a registry hack to restore that from some tech article/blog post/ etc, nothing in that waste of the Win 11 Settings app.
But with a visible scrollbar you would have a visible indication which behavior you triggered. If the scrollbar is invisible you get a changed viewport in both cases but you have to infer which gesture triggers which behavior.
But these are separate issues. For example, even with the scrollbars there can be a change between two behaviors: click on the empty bar jumps to that % or jumps by 1 page. And one can be a click and another a Shift-Click - where in the OS would you discover that??? And the scrollbar width - can only find a registry hack to restore that from some tech article/blog post/ etc, nothing in that waste of the Win 11 Settings app.