I use Scrivener to organize my notes, among other things, and have a list of files in my binder that I would like to organize by placing a few horizontal lines between them. Sure, the same thing can be arranged by using color labels for different groups of files, but I don’t really like that option.
You could just create a document and entitle it “------------”, then un-tick “Include in Compile”. The binder isn’t really something that is conducive to line separators given that it is a structured outline. In outlines, items are usually organised by hierarchy, with different groups being placed in different folders rather than divided by lines.
All the best,