Maybe I just don’t understand what you’re saying. If I double-click on the divider, doesn’t that accomplish the same thing as clicking the widget?
I think you only really bump into this issue if you have scroll bar appearance set to “always”, as I and the author of the link do.
Compare the first two screenshots in the link. The little parallel lines that you click or grab to resize are hidden by the horizontal slider. This only applies when the horizontal slider needs to appear in the scrollbar of course. This has been really bugging me.
If you don’t have scroll bars set to “always” (as presumably you don’t) then the option to grab or double click the divider line anywhere works. I shall leave scroll bars off for now as this is much preferable.
The bug is fixed in 26.3