About that unused button:
----====( /dev/input/event3 )====----
Name: "gpio-keys"
ID: bus 0x19, vendor, 0x1, product 0x1, version 0x100
Type 0x00 (EV_SYN)
Type 0x01 (EV_KEY)
KEY_VOLUMEDOWN KEY_01c9
# evdev_trace -t 3
/dev/input/event3: 1653585089.064 - 0x01/EV_KEY - 0x1c9/KEY_01c9 - 1
/dev/input/event3: 1653585089.064 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0
/dev/input/event3: 1653585089.231 - 0x01/EV_KEY - 0x1c9/KEY_01c9 - 0
/dev/input/event3: 1653585089.231 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0