The RadImageEditorUI's tools (selection, shape, text, etc.) have different UI element representing their settings. Those are hosted in a settings panel. In case there are many options that cannot fit in the vertical size of the control, a scrollbar should get displayed. One example of this is the SelectionTool.

In the Office2019 and VisualStudio2019 themes, the vertical scrollbar doesn't get displayed.

To work this around, extract the ControlTemplate of SettingsPanel control. Then find the first RowDefinition of the root Grid panel and change its Height from Auto to star ( * ).

<Style TargetType="telerik:ToolSettingsPanel">	
	<Setter Property="Template">
		<Setter.Value>
			<ControlTemplate TargetType="telerik:ToolSettingsPanel">
				<Grid Background="{TemplateBinding Background}">
					<Grid.RowDefinitions>
						<RowDefinition Height="*"/>
						<RowDefinition Height="Auto"/>
					</Grid.RowDefinitions>
<!-- other xaml here -->