I can only assume that when you spawn the blocks, you have something to determine how many you are spawning. If so, when you’ve spawned the blocks, set the variable to = the amount of blocks you have spawned
Everytime a block is destroyed, deduct 1 and do a check to see if the variable now = 0. If so, you Win the game.
Depending on how your BP’s communicate, you could always store the variable inside your game instance, that way you can access it from anywhere.