您可以使用DataGrid的SelectionChanged事件：

private SolidColorBrush DataGridRowSelectedForegroundBrush { get; set; } = new(Colors.LightGreen);

private void DataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    if (sender is not DataGrid dataGrid)
    {
        return;
    }

    // DataGridRow has an "IsSelected" property but it's internal.
    // We can use Reflection to get this property.
    Type dataGridRowType = typeof(DataGridRow);
    PropertyInfo? isSelectedProperty = dataGridRowType.GetProperty("IsSelected", BindingFlags.Instance | BindingFlags.NonPublic);

    foreach (DataGridRow dataGridRow in dataGrid.FindDescendants().OfType<DataGridRow>())
    {
        if (isSelectedProperty?.GetValue(dataGridRow) is bool isSelected &&
            isSelected is true)
        {
            dataGridRow.Foreground = DataGridRowSelectedForegroundBrush;
            continue;
        }

        dataGridRow.Foreground = dataGrid.Foreground;
    }
}

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顺便说一句，我正在使用CommunityToolkit.WinUI.UINuGet包来使用FindDescendants()。