@Rayenblue Yes, from your IDE image COM3 is the correct name. I would use it direct. The list()[] method works but the list can change if any other devices are added/removed. Is your Arduino a real one? The cheap Chinese ones take a different COMn number in different USB sockets.
Have you added the print as @glv said? Is anything printing?
The Ard sketch only sends every 100 mS. If you press and release the button quickly it may happen within 100 mS and be ignored. I think for the quiz you will find it too slow to react. The 100 delay at the end of the Ard sketch is too big. Suggest you change it to 40 mS. You could go less but it must be greater than the loop delay of the Processing, and we don’t know that yet. Once you get it working I think we should alter the Ard sketch to send on change, and on a slow frequency.