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.
If you have any further questions regarding your plans, please open a Support Ticket here so that we can better assist you. While we do our best to answer forum threads quickly, it can take up to a few days. Whereas support ticket guarantees a response in <24 hours.
Lance | Manager Technical Support
Virtual Classroom, the free self-paced technical training that gets you up to speed with Telerik and Kendo UI products quickly just got a fresh new look + new and improved content including a brand new Blazor course! Check it out at https://learn.telerik.com/.