Hi Richard,
There is a
Feature request logged for FileExplorer. It is logged for MVC, but as both Telerik UI for ASP.NET MVC and Telerik UI for ASP.NET Core are server-side wrappers of Kendo UI, they use one and the same Kendo UI widgets, which need to be implemented initially. You may vote for it to increase its priority for planning. Currently its implementation is not planned.
Regards,
Dimitar
Progress Telerik