[Windows] Fix SearchBar icon not updating on runtime theme changes

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

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.SearchBarThemeIssue"
+             Title="SearchBar Theme Issue Test">
+
+    <StackLayout Padding="20">
+        <Label Text="Test: SearchBar icon should change color when switching themes at runtime" 
+               FontSize="16" 
+               Margin="0,0,0,20"/>
+
+        <SearchBar x:Name="testSearchBar" 
+                   Text="Search" 
+                   Placeholder="Enter search text"
+                   WidthRequest="400" 
+                   Margin="0,0,0,20"/>
+
+        <Button x:Name="changeThemeButton"
+                Text="Switch to Dark Theme" 
+                WidthRequest="400"
+                Clicked="OnChangeThemeClicked" 
+                Margin="0,0,0,10"/>
+
+        <Button x:Name="resetThemeButton"
+                Text="Switch to Light Theme" 
+                WidthRequest="400"
+                Clicked="OnResetThemeClicked" 
+                Margin="0,0,0,20"/>
+
+        <Label x:Name="statusLabel" 
+               Text="Current theme: Light" 
+               FontSize="14"/>
+    </StackLayout>
+
+</ContentPage>

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

@@ -0,0 +1,22 @@
+namespace Maui.Controls.Sample.Issues
+{
+    public partial class SearchBarThemeIssue : ContentPage
+    {
+        public SearchBarThemeIssue()
+        {
+            InitializeComponent();
+        }
+
+        private void OnChangeThemeClicked(object sender, EventArgs e)
+        {
+            Application.Current.UserAppTheme = AppTheme.Dark;
+            statusLabel.Text = "Current theme: Dark";
+        }
+
+        private void OnResetThemeClicked(object sender, EventArgs e)
+        {
+            Application.Current.UserAppTheme = AppTheme.Light;
+            statusLabel.Text = "Current theme: Light";
+        }
+    }
+}

src/Core/src/Handlers/SearchBar/SearchBarHandler.Windows.cs

@@ -1,5 +1,6 @@
 #nullable enable
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.Maui.Controls;
 
 namespace Microsoft.Maui.Handlers
 {
@@ -24,6 +25,10 @@ protected override void ConnectHandler(AutoSuggestBox platformView)
 			// To address this, I have specifically handled the focus and unfocus events for AutoSuggestBox here. 
 			platformView.GotFocus += OnGotFocus;
 			platformView.LostFocus += OnLostFocus;
+
+			// Subscribe to theme changes to update QueryIcon
+			if (Microsoft.Maui.Controls.Application.Current is not null)
+				Microsoft.Maui.Controls.Application.Current.RequestedThemeChanged += OnAppThemeChanged;
 		}
 
 		protected override void DisconnectHandler(AutoSuggestBox platformView)
@@ -33,6 +38,10 @@ protected override void DisconnectHandler(AutoSuggestBox platformView)
 			platformView.TextChanged -= OnTextChanged;
 			platformView.GotFocus -= OnGotFocus;
 			platformView.LostFocus -= OnLostFocus;
+
+			// Unsubscribe from theme changes
+			if (Microsoft.Maui.Controls.Application.Current is not null)
+				Microsoft.Maui.Controls.Application.Current.RequestedThemeChanged -= OnAppThemeChanged;
 		}
 
 		public static void MapBackground(ISearchBarHandler handler, ISearchBar searchBar)
@@ -166,5 +175,19 @@ void OnLostFocus(object sender, UI.Xaml.RoutedEventArgs e)
 		{
 			UpdateIsFocused(false);
 		}
+
+		void OnAppThemeChanged(object? sender, AppThemeChangedEventArgs e)
+		{
+			UpdateQueryIcon();
+		}
+
+		void UpdateQueryIcon()
+		{
+			if (PlatformView is not null)
+			{
+				// Update the QueryIcon to ensure it reflects the current theme
+				PlatformView.QueryIcon = new SymbolIcon(Symbol.Find);
+			}
+		}
 	}
 }