MainPage.xaml

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:dx="http://schemas.devexpress.com/maui"
             xmlns:local="clr-namespace:TabPage_GenerateItems"             
             x:Class="TabPage_GenerateItems.MainPage"
             >
    <ContentPage.Resources>
        <local:BoolToColorConverter x:Key="boolToColorConverter" TrueSource="White" FalseSource="#90FFFFFF"/>
    </ContentPage.Resources>
    <ContentPage.BindingContext>
        <local:MainViewModel/>
    </ContentPage.BindingContext>
    <dx:TabView ItemsSource="{Binding CarModelsByBrand}"
             SelectedItemIndex="{Binding SelectedIndex, Mode=TwoWay}"
             ItemHeaderMinWidth="90"
             ItemHeaderMaxWidth="360"
             HeaderPanelItemSpacing="8"
             HeaderPanelBackgroundColor="#1e88e5"
             HeaderPanelShadowHeight="3"
             HeaderPanelShadowRadius="3"
             IsSelectedItemIndicatorVisible="True"
             SelectedItemIndicatorColor="White">
        <dx:TabView.ItemHeaderTemplate>
            <DataTemplate>
                <Label
                    x:Name="label"
                    Margin="16,48,16,16"
                    HorizontalOptions="Center"
                    VerticalOptions="Center"
                    TextColor="{Binding IsSelected, Converter={StaticResource boolToColorConverter}}"
                    Text="{Binding BrandName}"
                    HorizontalTextAlignment="Center"
                    Padding="5,0"/>
            </DataTemplate>
        </dx:TabView.ItemHeaderTemplate>
        <dx:TabView.ItemTemplate>
            <DataTemplate>
                
                    <CollectionView ItemsSource="{Binding CarModels}">
                        <CollectionView.ItemTemplate>
                            <DataTemplate>
                                <Label Padding="5" Text="{Binding FullName}" />
                            </DataTemplate>
                        </CollectionView.ItemTemplate>
                    </CollectionView>
                
            </DataTemplate>
        </dx:TabView.ItemTemplate>
    </dx:TabView>    
</ContentPage>