Let me update you on my progress, as I have found a workaround for the scroll edge effect not being applied at all. If you enable the vertical scroller, then the edge effect is applied correctly (this still seems like a bug, since I think it ought to work regardless). Here is an example: scrollView.hasVerticalScroller = true scrollView.scrollerStyle = .overlay This doesn't solve the lack of an API for setting the type of edge effect, but at least it lets us have the edge effect at all.

I have done this programmatically in the suggested way, using a sidebar split view item, but the scroll edge effect is not applied unfortunately. Here is a simple example: https://git.sr.ht/~jonsterling/cocoa-bindings-template Would you mind having a look to see what you think is going wrong? I prefer not to do this in a Storyboard (dealing with outline views and their cells in the storyboard leads to a lot of weird and unfixable misplacef frame warnings from Xcode—even in Apple’s sample projects! Hence I prefer a programmatic approach).

Unfortunately, the edge effect doesn't appear to be set automatically when constructing the view hierarchy manually; see my example here: https://git.sr.ht/~jonsterling/cocoa-bindings-template. I can confirm that it is set when I use a storyboard to build up the view hierarchy, but I can't figure out what I am doing differently. Do let me know if you can spy what is happening. I have filed a radar here: FB19629432.