For future stumblers:
When the app is killed and opened by a custom URI, it doesn't trigger func scene(_:openURLContexts:) but by the normal startup function func scene(_:willConnectTo:options) where connectionOptions contains your urlContexts.
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
		let myRootController = Controller()
		
		window.rootViewController = myRootController
		self.window = window
		window.makeKeyAndVisible()
		self.handle(urlContexts)
}
func scene(_ scene: UIScene, openURLContexts urlContexts: Set<UIOpenURLContext>) {
		self.handle(connectionOptions.urlContexts)
}
private func handle(_ urlContexts: Set<UIOpenURLContext>) {
		if let url = urlContexts.first?.url{
				@Binding var _: String = url.absoluteString
				print(url.absoluteString)
				Controller.message = url.absoluteString
				print(Controller.message)
}
}