This article explains how to customize the badge appearance in the .NET MAUI TabView.

To fully customize the badge in the TabView, you can set the Type property in BadgeSettings to None. This allows you to customize the badge beyond predefined styles by explicitly specifying properties such as Background and TextColor.

<ContentPage ...
             xmlns:core="clr-namespace:Syncfusion.Maui.Core;assembly=Syncfusion.Maui.Core"
             xmlns:tabView="clr-namespace:Syncfusion.Maui.TabView;assembly=Syncfusion.Maui.TabView">
    <tabView:SfTabView x:Name="tabView" >
        <tabView:SfTabView.Items>
            <tabView:SfTabItem Header="Call" BadgeText="3">
                <tabView:SfTabItem.BadgeSettings>
                    <core:BadgeSettings Type="None" Background="GreenYellow" TextColor="Red" TextPadding="3"/>
                </tabView:SfTabItem.BadgeSettings>
                <tabView:SfTabItem.Content>
                    <ListView RowHeight="50">
                        <ListView.ItemsSource>
                            <x:Array Type="{x:Type x:String}">
                                <x:String>James</x:String>
                                <x:String>Richard</x:String>
                                <x:String>Michael</x:String>
                                <x:String>Alex</x:String>
                                <x:String>Clara</x:String>
                            </x:Array>
                        </ListView.ItemsSource>
                        <ListView.ItemTemplate>
                            <DataTemplate>
                                <ViewCell>
                                    <Grid Margin="10,5">
                                        <Label VerticalOptions="Start"
                                                        HorizontalOptions="Start"
                                                        TextColor="#666666"
                                                        FontSize="16"
                                                        Text="{Binding}" />
                                    </Grid>
                                </ViewCell>
                            </DataTemplate>
                        </ListView.ItemTemplate>
                    </ListView>
                </tabView:SfTabItem.Content>
            </tabView:SfTabItem>
        </tabView:SfTabView.Items>
    </tabView:SfTabView>
</ContentPage>

By setting Type to None in BadgeSettings, you gain complete control over the appearance of the badge in TabView.

Output