Mojave has some features I do not use. One of those is Stacks, the feature that groups your Desktop files into categories and stacks them for you. I keep a very lean, mean Desktop so I do not use this feature. Besides, it does not work in Path Finder, at least not yet. However, if you have lots of stuff on your Desktop, I recommend reading this article which contains a video on the in’s and out’s of Stacks.