There may be a time in your game when you want to use a custom cursor. You could probably hide the original cursor, add a widget to the screen and have it move to the cursor position in the viewport when moved. OR you could hijack an already used cursor to be your custom widget.

In the project settings, map a widget to override one of the already available cursors.

Then on your event (if not default) set the cursor to the one you overrode.

In this case when the slots are hovered it changes the mouse cursor to the Slot widget, displaying an empty slot.