Hi Neil,
The ListPicker is intentionally a single selection popup control that is meant for a fast and easy popup selection. See Xamarin List Picker Documentation | Selection | Telerik UI for Xamarin
If you want an experience that has multiple selection capability, take a look at the RadComboBox's Multiple Selection capability https://docs.telerik.com/devtools/xamarin/controls/combobox/combobox-selection#multiple-selection
You can put a RadComboBox inside a RadPopup to get a popup experience for your users that allow for a more advanced multiple selection experience.
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Regards,
Lance | Manager Technical Support
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