private void RadMultiColumnComboBox_Loaded(object sender, RoutedEventArgs e)
{
	var mccb = (RadMultiColumnComboBox)sender;            
	var selection = mccb.SelectedItem;
	mccb.SetCurrentValue(RadMultiColumnComboBox.SelectedItemProperty, null);
	mccb.SetCurrentValue(RadMultiColumnComboBox.SelectedItemProperty, selection);
}

private void TimePicker_ParseDateTimeValue(object sender, Telerik.Windows.Controls.ParseDateTimeEventArgs args)
{
    string input = args.TextToParse;

    DateTime res;
    bool isValueParsedSuccessfully = DateTime.TryParse(input, out res);

    if (isValueParsedSuccessfully)
    {
        args.Result = res;
    }
    else
    {
        args.IsParsingSuccessful = false;
    }
}

shape.Geometry = group.GetFlattenedPathGeometry();

<Window x:Class="WpfApp20.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp20" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Telerik.Windows.Themes.Windows11;component/Themes/System.Windows.xaml"/>
                <ResourceDictionary Source="/Telerik.Windows.Themes.Windows11;component/Themes/Telerik.Windows.Controls.xaml"/>
                <ResourceDictionary Source="/Telerik.Windows.Themes.Windows11;component/Themes/Telerik.Windows.Controls.Input.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <telerik:RadAutoCompleteBox/>
    </Grid>
</Window>