The File manager have two areas left one (navigation pane) and the central one (content pane). Right now, we can provide template for the columns using detailsViewSettings.columns. But this customization is not possible in navigation pane (left side).
As of now, EJ2 File Manager component navigation pane do not have support for Template. Need to add template support in EJ2 platform also.
Query : Customizations made in the details view settings needs to be reflected in the navigation pane also.