Hide FlyoutIcon when FlyoutBehavior set to disabled

src/Controls/src/Core/Compatibility/Handlers/Shell/Android/ShellToolbarTracker.cs

@@ -82,6 +82,7 @@ public ShellToolbarTracker(IShellContext shellContext, AToolbar toolbar, DrawerL
 			((IShellController)ShellContext.Shell).AddFlyoutBehaviorObserver(this);
 			ShellContext.Shell.Toolbar.PropertyChanged += OnToolbarPropertyChanged;
 			ShellContext.Shell.Navigated += OnShellNavigated;
+			ShellContext.Shell.PropertyChanged += HandleShellPropertyChanged;
 		}
 
 		void IShellToolbarTracker.SetToolbar(IToolbar toolbar)
@@ -182,6 +183,7 @@ protected override void Dispose(bool disposing)
 				((IShellController)ShellContext.Shell)?.RemoveFlyoutBehaviorObserver(this);
 				ShellContext.Shell.Toolbar.PropertyChanged -= OnToolbarPropertyChanged;
 				ShellContext.Shell.Navigated -= OnShellNavigated;
+				ShellContext.Shell.PropertyChanged -= HandleShellPropertyChanged;
 				UpdateTitleView(ShellContext.AndroidContext, _platformToolbar, null);
 
 				if (_searchView != null)
@@ -280,6 +282,12 @@ void OnShellNavigated(object sender, ShellNavigatedEventArgs e)
 			}
 		}
 
+		void HandleShellPropertyChanged(object sender, PropertyChangedEventArgs e)
+		{
+			if (e.Is(Shell.FlyoutIconProperty))
+				UpdateLeftBarButtonItem();
+		}
+
 		BackButtonBehavior _backButtonBehavior = null;
 		protected virtual void OnPagePropertyChanged(object sender, PropertyChangedEventArgs e)
 		{

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellPageRendererTracker.cs

@@ -89,6 +89,8 @@ protected virtual void HandleShellPropertyChanged(object sender, PropertyChanged
 		{
 			if (e.Is(VisualElement.FlowDirectionProperty))
 				UpdateFlowDirection();
+			else if (e.Is(Shell.FlyoutIconProperty))
+				UpdateLeftToolbarItems();
 		}
 
 		protected virtual void OnBackButtonBehaviorPropertyChanged(object sender, PropertyChangedEventArgs e)

src/Controls/tests/TestCases.HostApp/Issues/Issue20166.xaml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Shell xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue20166"
+             FlyoutIcon="groceries.png">
+    <FlyoutItem>
+        <ShellContent Title="Page 1">
+            <ContentPage Shell.FlyoutBehavior="Flyout">
+                <Button Text="Switch to page 2" AutomationId="button1" Clicked="Button1_Clicked"/>
+            </ContentPage>
+        </ShellContent>
+            <ShellContent x:Name="shellTab2" Title="Page 2">
+                <ContentPage Shell.FlyoutBehavior="Disabled"/>
+        </ShellContent>
+     </FlyoutItem>
+</Shell>

src/Controls/tests/TestCases.HostApp/Issues/Issue20166.xaml.cs

@@ -0,0 +1,24 @@
+using System;
+using System.ComponentModel;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.Github, 20166, "Custom FlyoutIcon visible although FlyoutBehavior set to disabled", PlatformAffected.Android | PlatformAffected.iOS)]
+	public partial class Issue20166 : Shell
+	{
+		public Issue20166()
+		{
+			InitializeComponent();
+		}
+
+		void Button1_Clicked(System.Object sender, System.EventArgs e)
+		{
+			CurrentItem = shellTab2;
+			Current.FlyoutIcon = String.Empty;
+		}
+
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue20166.cs

@@ -0,0 +1,24 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+public class Issue20166 : _IssuesUITest
+{
+	public Issue20166(TestDevice device)
+	: base(device) { }
+
+	public override string Issue => "Custom FlyoutIcon visible although FlyoutBehavior set to disabled";
+
+	[Test]
+	[Category(UITestCategories.FlyoutPage)]
+	public void ShouldHideCustomFlyoutIconWhenNavigatingToPageWithDisabledFlyout()
+	{
+		// Click button 1 to switch to the page with disabled flyout
+		_ = App.WaitForElement("button1");
+		App.Click("button1");
+
+		// 2. Verify that the flyout icon is not rendered.
+		VerifyScreenshot();
+	}
+}