I'm using Swift concurrency in my application. The application creates a window with a toolbar. NSToolbarDelegate must implement func toolbar( _ toolbar: NSToolbar, itemForItemIdentifier itemIdentifier: NSToolbarItem.Identifier, willBeInsertedIntoToolbar flag: Bool) -> NSToolbarItem? This method has to be nonisolated, otherwise you get a warning Main actor-isolated instance method 'toolbar(_:itemForItemIdentifier:willBeInsertedIntoToolbar:)' cannot be used to satisfy nonisolated protocol requirement This method is designed to create a new NSToolbarItem. Apple docs: Use this method to create new NSToolbarItem objects when the toolbar asks for them. However, NSToolbarItem is isolated on @MainActor, so you have to call its constructor on @MainActor, which is impossible to do from a nonisolated method and still return a value from that method. Is this a bug in the current version of AppKit or is there a workaround?