Another approach is to use the SelectionChanged event of RadMultiColumnComboBox control and its CloseDropDown() method if you have access to this API.
sender, SelectionChangeEventArgs e)
If this doesn't work for you, there is a solution shown in the following forum
Progress TelerikWant to extend the target reach of your WPF applications, leveraging iOS, Android, and UWP? Try UI for Xamarin
a suite of polished and feature-rich components for the Xamarin
framework, which allow you to write beautiful native mobile apps using a
single shared C# codebase.