Yes, I can reproduce your issue. You could report an issue at Maui Issue
Additionally, as TableView is a descendant of ListView, it could be superseded by ListView or CollectionView. So, I recommend using ListView as an alternative. You could try using ListView.Header to define the Header. ListView also provides you a ItemSource and ItemTemplate which makes the control more customized. I wrote a small demo for you as an example:

<ListView>
    <ListView.Header>     
        <StackLayout BackgroundColor="LightGray">
            <Label Margin="10,0,0,0"
                   Text="Example Text"
                   FontSize="12"
                   FontAttributes="Bold" />
        </StackLayout>
    </ListView.Header>
    <ListView.ItemsSource>
        <x:Array Type="{x:Type x:String}">
            <x:String>First Example</x:String>
            <x:String>Second Example</x:String>
        </x:Array>
    </ListView.ItemsSource>
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Label Text="{Binding .}" />
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

For more info, you could refer to .NET MAUI ListView
Hope it works for you. If you still have questions, feel free to ask.