Read the errors, they are quite literal.
Player Event graph you unconnected the Create Widget. Therefore it will not create the widget.
Thus the first error.
The next two refer to the “E” event to toggle visibility. Set Visibility needs a reference to a widget.
Widgets, anything UI based, should be managed in the controller class.
When you create a widget you want to store a reference to it.
Example…
You can tweak it to hide the widget on initial load. Then add an event to toggle visibility.
You have to tell the Set Visibility node which widget you want to work with. Hence the “Target” pin and reasoning for storing a reference.
UI elements do not belong in the inventory class.