[Solved] Grouping in Listbox

The ListBox component doesn't currently support this functionality. You can submit a feature request and vote for it here: https://feedback.telerik.com/blazor?categoryId=2758.

Based on a similar older request for their jQuery library (https://feedback.telerik.com/kendo-jquery-ui/1360491-add-ability-to-group-data-in-listbox), it seems unlikely that this feature will be implemented.

If you don't need features like drag-and-drop, you might consider using the MultiSelect component instead, which does support grouping:
https://www.telerik.com/blazor-ui/documentation/components/multiselect/grouping

Regards,
Anislav Atanasov