This answer IS useless. Consider I have two objects. First object enters the volume so the ‘Overlapped’ variable sets to true. Then the second object enters the volume (the variable will remain true). Now if one of the objects leave the volume, the ‘Overlapped’ variable sets to false while I still have an object inside. This answer only works if you can guarantee that only one object can be inside the volume at a time.
By the way, As so many have answered this question I would like to add another way to achieve this. You also can use a ‘multi box trace for objects’ node and set the start and end at the center of the trigger volume (with slightly changed the end vector) and set the half size to fit the volume. it will output an array of all objects that you have set and also can ignore specific types of actors.
Regards,