Yes. When the player is on the floor, the value of PlayerIsNotJumping is set to true. But, it’s not set to false when the player falls, only once the space bar is pressed.
However, you’re over complicating things:
Instead of that variable, just have the Space key is pressed condition, along with Player is on the floor. If you also simulate the jump key pressed as the action, then that should be all you need (if you don’t simulate jump key pressed, then you’ll need to include a trigger once condition).
there is a condition named “is jumping”, checking if the platformer object is jumping. Pairing that with the trigger once creates the jump sound perfectly, as in how a button press let’s the sound happen in any situation of the game.