combine the titlebaar behavior with code behind

I made a title bar class, that inherits from title bar, which is a new control introduced, in .net 9

namespace METROWIND
{
    public class AppTitleBar: TitleBar
    {
        public SfComboBox ComboBox { get; set; }

        public AppTitleBar()
        {
            ComboBox = CreateComboBox()!;

            Icon = "icon_win.png";
            Title = "METROWIND";
            BackgroundColor = Color.FromArgb("#FF3C155F");
            HeightRequest = 48;
            Content = ComboBox;
        }

        private SfComboBox? CreateComboBox()
        {
            return new SfComboBox
            {
                Margin = new Thickness(5),
                IsEditable = true,
                IsClearButtonVisible = false,
                HighlightedTextColor = Colors.Red,
                HighlightedTextFontAttributes = FontAttributes.Bold,
                IsFilteringEnabled = true,
                TextHighlightMode = OccurrenceMode.MultipleOccurrence
            };
        }

        public void UpdateItemSource(
            IEnumerable<object> itemSouce,
            string displayMemberPath,
            string textMemberPath)
        {
            ComboBox!.ItemsSource = itemSouce;
            ComboBox!.DisplayMemberPath = displayMemberPath;
            ComboBox.TextMemberPath = textMemberPath;
        }
    }
}

I also created a method for update the itemsouce and the bindigns

Explanation

As you can see, every page has their own title bar

public partial class TurbinesCollectionPage: ContentPage
{
    public TurbinesCollectionPageViewModel PageViewModel { get; }

    public TurbinesCollectionPage(TurbinesCollectionPageViewModel
        turbinesCollectionPageViewModel)
    {
        InitializeComponent();

        PageViewModel = turbinesCollectionPageViewModel;

        PageViewModel.ColletionComboBox = combobox;
        PageViewModel.TurbinesCollection = TurbineCollection;

        BindingContext = turbinesCollectionPageViewModel;

        var tb = new AppTitleBar();
        tb.UpdateItemSource(PageViewModel.TurbinePins,
            "Turbine.Name", "Turbine.Name");
        App.WindowInstance!.TitleBar = tb;
        PageViewModel.ColletionComboBox = tb.ComboBox;
        tb.ComboBox.SelectionChanged += ComboBox_SelectionChanged;


        DeviceHelper.AddOrRemoveContentBasedOnDevice(MobileContent);

    }

    private void ComboBox_SelectionChanged(object? sender,
        Syncfusion.Maui.Inputs.SelectionChangedEventArgs e)
    {
        PageViewModel.SelectedItemChangeCommand.Execute(null);

        combobox.SelectedValue = string.Empty;
    }
}

This page has a combobox, that is used by mobile, to pick the turbine

<ContentPage
    x:Class="METROWIND.Views.TurbinesCollectionPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:editors="clr-namespace:Syncfusion.Maui.Inputs;assembly=Syncfusion.Maui.Inputs"
    xmlns:fonts="clr-namespace:METROWIND.Constants"
    xmlns:inputLayout="clr-namespace:Syncfusion.Maui.Core;assembly=Syncfusion.Maui.Core"
    xmlns:mct="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
    xmlns:model="clr-namespace:METROWIND.Models"
    xmlns:rex="clr-namespace:METROWIND.Resources"
    xmlns:vm="clr-namespace:METROWIND.ViewModel"
    x:Name="CollectionPage"
    x:DataType="vm:TurbinesCollectionPageViewModel"
    HideSoftInputOnTapped="True">

    <VerticalStackLayout Spacing="-20">
        <inputLayout:SfTextInputLayout
            x:Name="MobileContent"
            Style="{x:StaticResource TurbineCollectionComboBoxStyle}">
            <editors:SfComboBox
                x:Name="combobox"
                DisplayMemberPath="Turbine.Name"
                ItemsSource="{x:Binding TurbinePins}"
                Style="{x:DynamicResource TurbinesCollectionComboBoxStyle}">
                <editors:SfComboBox.Behaviors>
                    <mct:EventToCommandBehavior
                        Command="{x:Binding SelectedItemChangeCommand}"
                        EventName="SelectionChanged" />
                </editors:SfComboBox.Behaviors>
            </editors:SfComboBox>
        </inputLayout:SfTextInputLayout>

and a viewModel, to handle the logic

    public partial class TurbinesCollectionPageViewModel(
        ITurbineService turbineService,
        IAppService appService,
        IServiceProvider serviceProvider,
        ICommandHandler commandHandler,
        IConnectivity connectivity,
        NoInternetPopUp noInternetPopUp):
        AppShellViewModel(turbineService, appService, serviceProvider,
            commandHandler, connectivity, noInternetPopUp)
    {
        public CollectionView? TurbinesCollection;
        public SfComboBox? ColletionComboBox;

        [ObservableProperty]
        Turbine? turbine;

        [RelayCommand]
        async Task SelectedItemChange()
        {
            if (ColletionComboBox!.SelectedIndex == -1)
            {
                return;
            }

            var item = TurbinePins.ElementAt(
                ColletionComboBox.SelectedIndex);

            TurbinesCollection?.ScrollTo(ColletionComboBox.SelectedIndex,
                -1, ScrollToPosition.Center);

            var inputView = ColletionComboBox.Children[1] as Entry;

#if ANDROID || IOS
            if (KeyboardExtensions.IsSoftKeyboardShowing(inputView!))
            {
                await Task.Delay(200);
                await inputView!.HideKeyboardAsync(default);
            }
#else
            await Task.CompletedTask;
#endif
        }

The Question

As you can see, I have a title bar on this page, that does the exact as viewmodel. I need a way to remove the one from the code behind.

The potential problem that I face, is that I have 2 conboboxes, so I need to use the sae one for both