With a simple SwiftUI layout that presents a list of tasks that can present a detail view, there appears to be no way to configure the toolbar when running on Mac Catalyst.
Presenting in a NavigationView with columns gives the sidebar a toolbar that can be configured but the detail view will not have one and there is no way to add one. It will, instead, default to using iPad style toolbars which are inappropriate for macOS.
.windowToolbarStyle is unavailable to Catalyst apps.
Will this be addressed in macOS 13/iOS 16?