在DefaultButtonStyle（generic.xaml）中可以看到，VisualStatePointerOver将Button的Background更改为名为ButtonBackgroundPointerOver的ThemeResource。
（如果您不知道如何找到generic.xaml，请检查answer。
您可以像这样覆盖ButtonBackgroundPointerOver：

<Button>
    <Button.Resources>
        <Button.Resources>
            <SolidColorBrush
                x:Key="ButtonBackgroundPointerOver"
                Color="HotPink" />
        </Button.Resources>
    </Button.Resources>
</Button>

不幸的是，Button控件没有用于聚焦事件的VisualState。你可以做的是在代码隐藏中使用GotFocus和LostFocus事件来更改Button的Background，但你也可以创建一个自定义控件：

AwesomeButton.cs

public class AwesomeButton : Button
{
    public static readonly DependencyProperty FocusedBackgroundProperty =
        DependencyProperty.Register(
            nameof(FocusedBackground),
            typeof(Brush),
            typeof(AwesomeButton),
            new PropertyMetadata(default));

    public AwesomeButton()
    {
        GotFocus += AwesomeButton_GotFocus;
        LostFocus += AwesomeButton_LostFocus;
    }

    public Brush FocusedBackground
    {
        get => (Brush)GetValue(FocusedBackgroundProperty);
        set => SetValue(FocusedBackgroundProperty, value);
    }

    private Brush? BackgroundBeforeGettingFocus { get; set; }

    private void AwesomeButton_GotFocus(object sender, RoutedEventArgs e)
    {
        BackgroundBeforeGettingFocus = Background;
        Background = FocusedBackground;
    }

    private void AwesomeButton_LostFocus(object sender, RoutedEventArgs e)
    {
        Background = BackgroundBeforeGettingFocus;
    }
}

然后像这样使用它：

<local:AwesomeButton
    x:Name="AwesomeButton"
    Width="{x:Bind Width}"
    Height="{x:Bind Height}"
    HorizontalAlignment="Center"
    VerticalAlignment="Center"
    Background="Transparent"
    BorderThickness="0"
    FocusedBackground="LightGreen">
    <Button.Resources>
        <SolidColorBrush
            x:Key="ButtonBackgroundPointerOver"
            Color="HotPink" />
    </Button.Resources>
    <StackPanel
        HorizontalAlignment="Center"
        VerticalAlignment="Center"
        Orientation="Vertical">
        <FontIcon
            VerticalAlignment="Center"
            FontFamily="{StaticResource SymbolThemeFontFamily}"
            FontSize="{x:Bind IconSize}"
            Glyph="{x:Bind Glyph}" />
        <TextBlock
            Margin="0,10,0,0"
            HorizontalAlignment="Center"
            VerticalAlignment="Center"
            FontSize="{x:Bind FontSize}"
            Text="{x:Bind Label}" />
    </StackPanel>
</local:AwesomeButton>