How do I customize the appearance of tabs in .NET MAUI?

You can customize the appearance of tabs by defining a custom style for the TabbedPage like this:
XAML

<TabbedPage xmls="http://schemas.microsoft.com/dotnet/2021/maui"
            Xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
        <TabbedPage.Resources>
            <Style TargetType="TabbedPage">
                <!-- Your custom styles here -->
            </Style>
        </TabbedPage.Resources>
       <!-- Add tab pages here -->
</TabbedPage>