When trying to show the RadRichTextBox' LineNumberingDialog, nothing is displayed. This happens when using the NoXaml Telerik dlls and themes other than Windows11. The dialog is shown only in the Windows11 theme.
To work this around, add the following two lines in the App.xaml resources.
<Application x:Class="WpfApp1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApp1"
xmlns:telerikDialogs="clr-namespace:Telerik.Windows.Controls.RichTextBoxUI.Dialogs;assembly=Telerik.Windows.Controls.RichTextBox"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/System.Windows.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.ImageEditor.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.Navigation.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.Input.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.RibbonView.xaml"/>
<ResourceDictionary Source="/Telerik.Windows.Themes.Fluent;component/Themes/Telerik.Windows.Controls.RichTextBox.xaml"/>
</ResourceDictionary.MergedDictionaries>
<Style TargetType="telerikDialogs:LineNumberingDialog" BasedOn="{StaticResource RadWindowStyle}"/>
<Style TargetType="telerikDialogs:LineNumberingDistanceNumericUpDown" BasedOn="{StaticResource RadNumericUpDownStyle}"/>
</ResourceDictionary>
</Application.Resources>
</Application>