MainPage.xaml

<FlyoutPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="DrawerViewExample.MainPage"
             xmlns:local="clr-namespace:DrawerViewExample"
             
             FlyoutLayoutBehavior="{Binding IsLandscapeOriented, Source={x:Reference page}, 
                                    Converter={StaticResource boolToDrawerBehaviorConverter}}"
             x:Name="page">
    <FlyoutPage.BindingContext>
        <local:MainViewModel/>
    </FlyoutPage.BindingContext>
    <FlyoutPage.Flyout>
        <ContentPage Title="About" IconImageSource="hamburger" WidthRequest="50">
            <CollectionView x:Name="carBrandList" 
                            ItemsSource="{Binding CarModelsByBrand}" SelectionMode="Single">
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <Label Padding="5" Text="{Binding BrandName}" />
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>
        </ContentPage>
    </FlyoutPage.Flyout>
    <FlyoutPage.Detail>
        <NavigationPage WidthRequest="50">
            <x:Arguments>
                <ContentPage>
                    <CollectionView BindingContext="{x:Reference carBrandList}"
                                ItemsSource="{Binding SelectedItem.CarModels}">
                        <CollectionView.ItemTemplate>
                            <DataTemplate>
                                <Label Padding="5" Text="{Binding FullName}" />
                             </DataTemplate>
                        </CollectionView.ItemTemplate>
                    </CollectionView>
                </ContentPage>
            </x:Arguments>
        </NavigationPage>
    </FlyoutPage.Detail>
</FlyoutPage>