I've built my off panel widget (A custom splash screen) and it's working great in the developer edition. I've also added it to a ArcGIS Portal installation by including the widget in:
This appears to be working and I can create new applications with the new widget. Existing sites it doesn't appear as configurable in the Portal WAB (until after you modify the JSON of the item manually).
If I add my widget to Portal using the normal method of putting the custom widgets in a shared virtual directory and adding them as an 'app extension' they seem to only behave as on panel widgets. http://enterprise.arcgis.com/en/portal/10.5/use/add-custom-widgets.htm
Is this true or is this shared virtual directory supposed to work with off panel widgets too. I thought I read somewhere it isn't supported.
Other than being unsupported has anyone else used the method of pasting in a custom widget into the folders listed above? What is the gotcha that is being missed using this method?