Displaying items count on each group header

The total number of items in each group will be displayed in the group header by binding the Count property in the SfListView.GroupHeaderTemplate.

<ContentPage xmlns:syncfusion="clr-namespace:Syncfusion.ListView.XForms;assembly=Syncfusion.SfListView.XForms"
             xmlns:data="clr-namespace:Syncfusion.DataSource;assembly=Syncfusion.DataSource.Portable">
 <syncfusion:SfListView>
  <syncfusion:SfListView.GroupHeaderTemplate>
    <DataTemplate>
     <Grid BackgroundColor="#E4E4E4">
      <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
      </Grid.ColumnDefinitions>
      <StackLayout Orientation="Horizontal" HorizontalOptions="Start"
                   VerticalOptions="Center" >
        <Label Text="{Binding Key}" TextColor="Black" />
        <Label Text="Year" TextColor="Black" />
      </StackLayout>
      <StackLayout Orientation="Horizontal" Grid.Column="1"
                   HorizontalOptions="EndAndExpand" VerticalOptions="Center">
        <Label Text="{Binding Count}" TextColor="Black" />
        <Label Text="Item(s)" TextColor="Black" />
      </StackLayout>
     </Grid>
    </DataTemplate>
  </syncfusion:SfListView.GroupHeaderTemplate>
 </syncfusion:SfListView>
</ContentPage>

To know more about groupig in SfListView, please refer our documentation here