@marioguzman @brentsimmons If you want more control, gotta use the deprecated NavigationView with a List {}.listStyle(.sidebar) in the first column, then you have more options, including adding that sidebar button via .toolbar {}. (Maybe there'll be a fix before NavigationView disappears.) But it's still not going to satisfy longtime AppKit folks (or macOS interaction aficionados). For example, no cool slide animation if you disappear the detail view, etc. How do you grab a collapsed column? No control of the sliders. If SwiftUI doesn't save the state, well....
"How can I do all the cool AppKit things in SwiftUI" will drive you crazy. "How can I design to work within SwiftUI constraints" might be kind of fun if you enjoy a "constraints spur creativity" mode. Another gotcha: You MUST have a sidebar when you use NavigationSplitView.