Fix Changing Shell.NavBarIsVisible does not update the nav bar

src/Controls/src/Core/Shell/BaseShellItem.cs

@@ -250,6 +250,18 @@ internal static void PropagateFromParent(BindableProperty property, Element me)
 			if (me == null || me.Parent == null)
 				return;
 
+			// For Shell.NavBarIsVisibleProperty, find the shell instance for more accurate propagation
+			if (property == Shell.NavBarIsVisibleProperty)
+			{
+				var shell = me.FindParentOfType<Shell>();
+				if (shell is not null && shell.IsSet(property))
+				{
+					// Get the value from the Shell directly
+					me.SetValue(property, shell.GetValue(property));
+					return;
+				}
+			}
+
 			Propagate(property, me.Parent, me, false);
 		}
 

src/Controls/src/Core/Shell/Shell.cs

@@ -76,7 +76,17 @@ private static void OnNavBarIsVisibleChanged(BindableObject bindable, object old
 				?? (bindable as BaseShellItem)?.FindParentOfType<Shell>()
 				?? (bindable as Page)?.FindParentOfType<Shell>();
 
-			shell?.OnPropertyChanged(NavBarIsVisibleProperty.PropertyName);
+			if (shell != null)
+			{
+				// Notify about the property change
+				shell.OnPropertyChanged(NavBarIsVisibleProperty.PropertyName);
+
+				// Explicitly propagate the property change to all children
+				if (shell is IPropertyPropagationController controller)
+				{
+					controller.PropagatePropertyChanged(NavBarIsVisibleProperty.PropertyName);
+				}
+			}
 		}
 
 		/// <summary>

src/Controls/tests/TestCases.HostApp/Issues/Issue17550.cs

@@ -0,0 +1,57 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 17550, "Changing Shell.NavBarIsVisible does not update the nav bar on Mac / iOS",
+	PlatformAffected.UWP)]
+public class Issue17550 : TestShell
+{
+	Button _toggleButton;
+
+	protected override void Init()
+	{
+		// Create a toggle button similar to the one in SandboxShell.xaml
+		_toggleButton = new Button
+		{
+			Text = Shell.GetNavBarIsVisible(this) ? "Hide NavBar" : "Show NavBar",
+			HeightRequest = 50,
+			WidthRequest = 150,
+			AutomationId = "NavBarToggleButton",
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center
+		};
+
+		_toggleButton.Clicked += OnNavBarToggleButtonClicked;
+
+		// Add the button to a content page in the shell
+		Items.Add(new ShellContent
+		{
+			Content = new ContentPage
+			{
+				Title = "Home",
+				Content = new StackLayout
+				{
+					Children =
+						{
+							new Label
+							{
+								Text = "Toggle NavBar visibility",
+								HorizontalOptions = LayoutOptions.Center
+							},
+							_toggleButton
+						},
+					VerticalOptions = LayoutOptions.Center
+				}
+			}
+		});
+	}
+
+	void OnNavBarToggleButtonClicked(object sender, EventArgs e)
+	{
+		// Toggle the NavBar visibility
+		bool isCurrentlyVisible = Shell.GetNavBarIsVisible(this);
+		bool newVisibility = !isCurrentlyVisible;
+		Shell.SetNavBarIsVisible(this, newVisibility);
+
+		// Update the button text to reflect the new state
+		_toggleButton.Text = newVisibility ? "Hide NavBar" : "Show NavBar";
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue17550.cs

@@ -0,0 +1,28 @@
+using NUnit.Framework;
+using NUnit.Framework.Legacy;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+public class Issue17550 : _IssuesUITest
+{
+	public Issue17550(TestDevice device) : base(device) { }
+	public override string Issue => "Changing Shell.NavBarIsVisible does not update the nav bar on Mac / iOS";
+
+	[Test, Order(1)]
+	[Category(UITestCategories.Shell)]
+	public void VerifyNavBarStatusAtInitialLoading()
+	{
+		App.WaitForElement("NavBarToggleButton");
+		VerifyScreenshot();
+	}
+
+	[Test, Order(2)]
+	[Category(UITestCategories.Shell)]
+	public void VerifyNavBarStatusAtRuntime()
+	{
+		App.WaitForElement("NavBarToggleButton");
+		App.Tap("NavBarToggleButton");
+		VerifyScreenshot();
+	}
+}