I installed the latest EB developer platform and if I open up a template (e.g. Dart), unlock "Lock layout" and add a web map. However, it seems I cannot add any Layout widget to the map (e.g. Sidebar widget). When I try dragging any such widget to the map, there is a X symbol indicating it cannot be added.
I've gone through Esri's EB documentation on widgets, including the Layout widgets, and it is unclear why I am seeing this behavior.