There are several different ways to do this, I did something similar in opening a door for a school project where I counted down how many keys were left in the level to open a door, to start I made the key (pickup) check for an overlap of anyone tagged friendly which is my player, then I casted to the game mode where I made a function which set my number of keys picked up by +1, then in the door I did a branch comparing how many keys are needed for that door to be open, from a do once node I then fired the function that this door served which was opening the door, for you that would fire off the end game sequence, however youve either done that or are planning on doing that.
The end goal is different but the logic between the two projects is so similar you would just have to slightly change a few easy values to match your goal.
Should not that the function is in the game mode because I needed its value to be seperate from the door and the key objects.
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